140slides.pdf

60-140
Introduction to Algorithms and Programming I
FALL 2015
 FALL 2015
INSTRUCTOR: DR. C.I. EZEIFE
Everybody
knows that the
WORLD’S COOLEST
STUDENTS TAKE
60-140
SCHOOL OF COMPUTER SCIENCE
SCHOOL OF COMPUTER SCIENCE,
UNIVERSITY OF WINDSOR
60-140 Dr. C.I. Ezeife © 2015 Slide 1

1 O i f C t S t
1. Overview of Computer Systems
 Computers are classified based on their generation and
type.
 The architecture of different generations of computers
 The architecture of different generations of computers
differ with advancement in technology.
 Changes in computer equipment have gone through
four generations namely:
• First Generation Computers (1945-1955): Bulky,
expensive consumed a lot of energy because main
expensive, consumed a lot of energy because main
electronic component was vacuum tube. Pro-
gramming was in machine language and wiring up
l b d
plug boards.

O i f C t S t
Overview of Computer Systems
 Second Generation Computers (1955-1965): Basic
electronic components became transistors. Prog-
ramming in High level language with punched cards.
g g g g p
 Third Generation Computers (1965-1980): Basic
technology became integrated circuit (I Cs) allowing
t i t ili hi F t h d
many transistors on a silicon chip. Faster, cheaper and
smaller in size, e.g., IBM system 360.
 Fourth Generation (1980-1990): Personal Computers
( ) p
came to use. Technology in use is large scale
integration(LSI). Support for network and GUI.
 Higher Generations: Use of VLSI technology
 Higher Generations: Use of VLSI technology.

O i f C t S t
Overview of Computer Systems
Vacuum Tube, Transistor, an LSI chip

T f C t
Types of Computers
 Computers belong to one of these types based on their
size, processing power, number of concurrent users
supported and their cost.
pp
• Micro or Personal Computers - support only a
single user, very compact in size. Processing power
i i i b t till li it d h h d b
is increasing but still limited when shared by many
programs and users, e.g., IBM PC, laptops.
• Mini Computers (minis) - More processing power
p ( ) p g p
can be shared among multiple users, e.g., SUN
workstations. Generally, more expensive than micro
computers A network of minis used for
computers. A network of minis used for

T f C t
Types of Computers
implementing powerful virtual computing processing powers
implementing powerful virtual computing processing powers
like grid and cloud computing. Grid computing applies
resources of many computers to a single problem (European
Data Grid) while cloud computing is used for Internet based
computing (e g online web mail like GoogleApps) where
computing (e.g., online web mail like GoogleApps) where
resources and data are stored online and shared with users.
• Mainframe Computers – Generally, bigger than mini
computers, and support hundreds of users at a time, e.g., IBM
370
370.
• Super Computers - Used for high performance number-
crunching applications like processing satellite data from
space, e.g., Cray Jaguar with about 150,000 cores (CPUs)..
p , g , y g , ( )
 Every computer system is made up of hardware and software
components.

H d C t
Hardware Components
 The computer hardware consists of physical electronic
components for performing the following functions:
components for performing the following functions:
Function Component
• Data Storage -Primary memory (RAM
g y y (
and ROM).
-Secondary memory
(disks & CD-ROMs usb or
(disks & CD-ROMs, usb or
flash memory key, tapes)
• Data Processing Central Processing Unit (CPU)
• Input of Data Input devices, e.g, Keyboard,
mouse, web camera
O t t f D t O t t d i i t
• Output of Data Output devices, e.g., printer,
monitor, speakers

D t St i M i M
Data Storage in Main Memory
C t t i f ti ( d d t )
 Computers represent information (programs and data)
as patterns of binary digits (bits)
 A bit is one of the digits 0 and 1.
 Thus, to represent a bit, the hardware needs a device
capable of being in one of two states (e.g., a switch of
“on” for bit 1 and “off” for bit 0)
on for bit 1 and off for bit 0)
 Data and programs are represented as a string of
binary digits
E 9 + 6 i bi t d 00001001 d
 E.g., 9 + 6 in binary are represented as 00001001 and
00000110, then passed to an add circuit to produce
binary result.

D t St
Data Storage
 Bits of data are stored in memory and bit collections of
size 8 make 1 byte.
 A memory cell is made up of 1 to 4 bytes (ie. 8 bits to 32
 A memory cell is made up of 1 to 4 bytes (ie. 8 bits to 32
bits) depending on the word length of the system.
 1 kilobyte memory has 1024 bytes (approx 103 or 210)
 1 Megabyte memory has approx 106 or 220 bytes.
 1 Gigabyte memory has approx 109 or 230 bytes.
I di id l ll i hi ’ i id tifi d ith
 Individual cells in a machine’s main memory are identified with
unique names called addresses
 The addresses of 1MB memory are 0 through 1048575 if a memory
ll i j t 1 b t
cell is just 1 byte.

D t St i M
Data Storage in Memory
 Each cell of memory can be read or written (modified)
individually.
 RAM is volatile because information stored is lost on
 RAM is volatile because information stored is lost on
power off.
 Thus, secondary memories are used to store data for
future use (disks, CD-ROMs and tapes).
 At the user and program level, physical storage
addresses are commonly referenced using logical names
addresses are commonly referenced using logical names
or addresses like file names for block of data on disk,
and variable names for memory cells.

D t St
Data Storage
 While numeric data are represented in binary,
characters are represented using standard codes.
 One code is ASCII (American standard code for
 One code is ASCII (American standard code for
Information Interchange) which uses seven bits to
represent a character.
 Disks are a common storage device for storing
g g
information for future use. Storage space is generally
more available on disk which are cheaper per unit of
storage space than main memory
storage space than main memory.

Th C t l P i U it (CPU)
The Central Processing Unit (CPU)
 CPU is the part of the computer responsible for
fetching instructions and data from memory and
executing them.
g
 Central Processing Unit (CPU): Processes information,
arithmetic and logical (+, -, *, /, % and
l i l/ l ti l ti ( A d O N t))
logical/relational operations (e.g. And, Or, Not)).
 It receives instructions and data from input devices
which it stores in main memory.
y
 Later, it fetches these instructions and data from main
memory and executes them to produce output (results)

Th I t/O t t D i
The Input/Output Devices
 Input device accepts input from the user and thus has
mechanisms for converting characters into bits, e.g.,
keyboard or mouse.
y
O t t d i di l t t lt f i t
 Output device displays output or result of processing to
the user, e.g., printer or monitor.

S ft C t
Software Components
 The software system drives the physical hardware
components through a sequence of instructions called
programs.
p g
 There are many software systems in a computer
• (1) Operating Systems for managing computer
resources, e.g., UNIX, LINUX, MSDOS, Windows
2000/XP/Vista/7, Apple Macintosh OS X.
• (2) Compilers for translating high level language
(2) Compilers for translating high level language
programs to machine language (bits), e.g., C,
PASCAL compilers.

S ft S t
Software Systems
• (3) Network Software for allowing more than one
computer to be connected together and to share
information (e.g., SSH, SFTP, telnet, ftp).
( g , , , , p)
• (4) Productivity Tools for allowing users to perform
daily business and office operations in a more
d ti f hi ll d d ti it t l (
productive fashion called productivity tools (e.g.,
word processors, database, slide presentation and
spread sheet programs)
• (5) Others, e.g., utility applications like virus
checkers, games, etc.

Overview of Algorithms &
P i L
Programming Languages
 Computer Science as a field is involved with issues
p
related to
• algorithm definition, coding, refinement, analysis
and discovery
and discovery
• as well as issues related to simulation of human
intelligence.
A l ith i f t f l i ifi
 An algorithm is a sequence of steps for solving a specific
problem given its input data and the expected output
data.
 Examples of real-life algorithms are
• operating a laundry machine, playing a video game, baking a
cake

P i L
 Algorithms?
g
 Algorithms are executed by human beings or
computers. An example software for executing
l ith i RAPTOR hi h i il bl
algorithms is RAPTOR which is available on our cs
servers through NoMachine connection.
 When executed by people, an algorithm needs to be
W e e ecuted by peop e, a a go t eeds to be
presented at their level of understanding and in a
language they understand
Wh t d b hi ( t ) l ith
 When executed by machine (computer), an algorithm
also needs to be presented at its level of understanding
and in a language it understands.
g g

P i L
E l f l ith E l 1 1
 Example of an algorithm: Example 1.1
 Find the largest common divisor of 2 positive integers.
(The Euclidean algorithm)
• Begin
• Input: 2 positive integers, large and small
O t t th i l t di i (LCD)
• Output: their largest common divisor (LCD)
• Procedure:
– Step 1: Read large and small
p g
– Step 2: Remainder = large % small
– Step 3: If Remainder == 0

P i L
– then
• Step 3.11: LCD = small
• Step 3.12: Goto Step 4
p p
– else
• Step 3.21: large = small
S 3 22 ll R i d
• Step 3.22: small = Remainder
• Step 3.23: Go to Step 2
• Step 4: Output the LCD of large and small
p p g
• Step 5: End

P i L
 E.g., Find the largest common divisor of 40 and 16

Algorithms & Programming
L
Languages
 Focus of the course (60-140) is on how to discover
programs for solving a task (problem solving)
 To do this, we may need to first define the precise
 To do this, we may need to first define the precise
sequence of steps for solving this problem represented
as an algorithm in pseudocode.
 The computer does not understand pseudocode but a
program written in a computer language.
 Thus for the computer to execute our algorithm it
 Thus, for the computer to execute our algorithm, it
eventually needs to be translated into a program in a
computer language like C.

L
Languages
 Computer languages are machine language, assembly
language and high level languages.
 High level programming languages are easier to use by
 High level programming languages are easier to use by
humans since they are closest to English and Math.
 Current programming languages fall into one of the
following four programming paradigms:

L
Languages
LISP ML Scheme functional
Machine
langs
Fortran Basic C Ada
Cobol Algol APL Pacal
Simula C++ Ada95
procedural
/imperative
bj t
Simula C++ Ada95
Smalltalk Java
GPSS Prolog
object-
oriented
declarative
g

L
Languages
B f itt i hi h l l l i
 Before a program written in a high level language is
executed by the CPU, it needs to be translated, linked
and loaded into memory in a process called compilation
d li ki
and linking.
 Program preparation process is:
• Step 1. Type Source program in high level language
Step 1. Type Source program in high level language
(eg. C lang) using text editor (eg. pico filename.c)
• Step 2. Compile to get object program in machine
language using cc filename c
language using cc filename.c
• Step 3. Link to get load module
• Step 4. Load into memory to execute with ./a.out

Introduction to C Programming
L
Language
 A C source program file must be given a name with .c
extension, e.g., test.c and this file must be prepared
with a text editor like Unix/Linux vi editor, nedit, pico
, , p
or PC’s notepad or Visual C++ editor.
 A C compiler is used to compile a C program. To
il U i /Li fil
compile on Unix/Linux, use: cc filename.c
 Program instructions that violate the syntax or
grammar rules of C will cause syntax errors and must
g y
be corrected before a successful compilation is
achieved.

Introduction to C Programming
L
Language
Aft il ti th i t bt i th
 After compilation, the program is run to obtain the
desired result. On Unix/Linux, run with the command:
./a.out
 General structure of a simple C program is:
#include <stdio.h>
int main(void)
{
Variables declared here; /* in correct syntax*/
y
program instructions; // in correct syntax
return 0;
}
}

i C i
Introduction to C Programming Language
 #include <stdio h>
 #include <stdio.h>
/* Simple C program for finding the sum of two integers */
int main(void)
{
{
int num1, num2, sum;
printf("Type the two integers to sum :");
scanf("%d %d" &num1 &num2);
scanf( %d %d , &num1, &num2);
sum = num1 + num2;
printf("sum = %d n", sum);
return 0;
return 0;
}

i C i
Introduction to C Programming Language
T k Wi d d l t i t
 To work on Windows development environment, you
can download Microsoft Visual C++ compiler and
check section 1.8 of book on how to use it to type,
il li k d t
compile, link and execute your program.
 Note that sections on how to use pico and nedit text
editors on Unix/Linux are 1.5.2 and 1.5.3 of book
 Section on how to use SSH and SFTP is 1.6 of book.
 Section on Macintosh Personal computer is 1.7
N t th t h h t d ith ibl
 Note that each chapter ends with possible
programming errors and has a section on exercises
with solutions.

2 P bl S l i St
2. Problem Solving Steps
 Objectives
• Understand what a problem is
• Discuss six problem solving steps (RCMACT)
• Discuss six problem solving steps (RCMACT)
 Types of Problems
 1. Problems with Algorithmic Solutions
1. Problems with Algorithmic Solutions
• Have a clearly defined sequence of steps that would
give the desired solution
– E.g. baking a cake, adding two numbers

P bl S l i St
Problem Solving Steps
• the sequence of steps or recipe for arriving at the
solution is called the algorithm
 2. Problems with Heuristic Solutions
 2. Problems with Heuristic Solutions
• Solutions emerge largely from the process of trial
and error based on knowledge and experience
• E.g., winning a tennis game or a chess game, making
a speech at a ceremony
 Many problems will require a combination of the two
 Many problems will require a combination of the two
kinds of solution

P bl S l i St
I hi l d i h l i h i
 In this course, we are mostly concerned with algorithmic
problems.
• computers are good at solving such problems
 Heuristic problem solving (getting computers to speak English or
recognize patterns) is the focus of Artificial Intelligence
 What is a Problem?
• It has three main components of (i) input data set, (ii) desired
output data set and
p
• (iii) we want to define a sequence of steps (algorithm and/or
program) for transforming input data to desired output data.

P bl S l i St
 What is a problem’s algorithmic solution?
• the sequence of steps needed to reach the desired
output or the best output data expressed in
output or the best output data expressed in
pseudocode.
 What is a Program?
• the sequence of steps (algorithms) expressed(coded)
in a computer language like C.
bl i h Al i h i C d d i Desired output
problem with
input & output
Algorithmic
Solution
Coded into a
Program
Desired output
through computer

P bl S l i St
 Example 2.1: Management wants to see the patterns in
absenteeism across its two departments, dept1 and
dept2 for one week. It is interested in knowing the total
p g
absenteeism in each department in the one week it
collected data. You are required to identify the input
and output data of this problem and attempt to define
and output data of this problem and attempt to define
an algorithm and a program.

P bl S l i St

S i S ( C AC )
Problem Solving Steps (RCMACT)
1 D fi i th P bl R i t (R)
 1. Defining the Problem Requirements (R)
• clearly defining the problem in words, stating the input and
output data as well as the processing logic. It may need
knowledge or familiarity with a real life environment to
knowledge or familiarity with a real life environment to
understand the needs of a problem
 2. Identifying Problem Components (C)
• From the problem definition, identify the list of problem
From the problem definition, identify the list of problem
inputs, outputs, constraints and relationships between input
and output data expressed in coherent formulas.
 3. Possibly break problem solution into small modules (M)
• This step uses top-down design approach to solve a big
problem using structure chart. This step may be skipped for
small problems that do not need breaking down.

St i P bl S l i
Steps in Problem Solving
 4. Design the Algorithm to solve the problem (A)
• Best among many alternative ways for solving the
problem is chosen.
problem is chosen.
• Define algorithmic solution for all modules in
structure chart.
• E.g., solution that is most cost efficient, space
efficient or fastest.
 5 Implementation and Coding (C)
 5. Implementation and Coding (C)
• Translate the algorithmic solution from step 4 to C
programming language to obtain a program.
p g g g g p g

St i P bl S l i
Steps in Problem Solving
P h t b th l ( t ) f C d
• Programs have to obey the grammar rules (syntax) of C and
any violation results in a syntax error (called bug).
• A bug needs to be corrected during debugging before the
program is accepted by the compiler.
program is accepted by the compiler.
• Other types of error that might need to be corrected during
coding for correct results to be obtained are logic and runtime
errors.
• The C implementation of Example 2.1 is: (solve)
 6. Test or Evaluate the solution to ensure it produces desired
results(T)
• A set of complete test data is used to test the correctness of the
program by tracing the program/algorithm with hand and
running the program.

Diffi lti With P bl S l i
Difficulties With Problem Solving
 Failing to outline details of the solution (algorithm and
program) completely
 Failing to define the problem correctly
 Failing to define the problem correctly
 Failing to generate a sufficient list of alternatives
 Failing to use a logical sequence of steps in the solution
g g
 Poor evaluation of the solution (algorithm and
program)
Al b h d d
 Always remember that computer does not see and
needs to be given all details about what to do.

3. Types of Algorithmic and Program
Instructions
Instructions
Obj ti
 Objectives
 1. Introduce programming language concepts of
variables, constants and their data types
 2. Introduce types of algorithmic and program
instructions
 3 Discuss Read(scanf)/Print(printf) and Assignment
 3. Discuss Read(scanf)/Print(printf) and Assignment
instructions.
 Variables and Constants
 Variables and Constants are names for storage
locations (memory cells) holding data values processed
by the computer

Problem Solving Concepts
(V i bl d C t t )
(Variables and Constants)
 Programmers define data relevant to a problem as
constants or variables
 Variables and constants form building blocks for
 Variables and constants form building blocks for
equations and expressions used in problem solving.
 Both variables and constants have specific data types.
E.g., alphabetic or numerical value
 Differences Between Variables & Constants
• The value of a variable may change during
• The value of a variable may change during
processing of a problem in a program, but the value
of a constant cannot change

(V i bl d C t t )
Th f f d l i i bl i b h l i h d C
 The format for declaring variables in both an algorithm and a C
program is:
datatype variablename[,variablenames];
 The format for declaring constants in both an algorithm and a C
program is:
const datatype
variablename=value[,variablenames=values];
[, ];
A constant can also be defined using preprocessor directive:
#define constantname value

(V i bl d C t t )
 Example 3.1 : A class of ten students took a quiz. The
grades (integers in the range 0 to 100) for quiz are
available to you. Determine the class average on the
y g
quiz.
• Identify the constants and variables you need to
l thi bl
solve this problem

V i bl d C t t
Variables and Constants
 Show the variables and constants needed to solve these
problems.
 Example 3.3: You are required to count the number of
 Example 3.3: You are required to count the number of
60-140 students who have completed assignment #1.
The class has 250 students
 Example 3.4: Find the sum and product of 2 numbers.

I i V i bl /C t t
Issues concerning Variables/Constants
 Rules for naming variables/constants differ from
 Rules for naming variables/constants differ from
language to language. C allows unlimited number of
alphanumeric characters.
 It is good problem solving practice to use variable
names close to the meaning of its data values
 Multiple word variable names should be separated with
 Multiple word variable names should be separated with
underscore to make them more readable, e.g., asn1_140
 Use variable names with less than 15 characters to
avoid ambiguities.
 Check Table 3.1 of text for keyword names not to be
used as variable names in programs
used as variable names in programs.

D t T
Data Types
 Input Data are facts (values) used by the computer to
process algorithmic solutions and programs to a
problem while output data are the results (values)
p p ( )
produced by the computer after running the program.
I t D t
Computer steps Output
Input Data through algorithm
or program
p
Data
E.g.
Q i k Equations for finding
Class
A
Quiz marks Equations for finding
Sum & Average
Average

D t T
Data Types
D f diff
 Data are of many different types:
 1. Integer Data Type(called int or long int in C): Integers (whole
numbers, e.g., 1577, -18). Arithmetic operations can be performed
thi d t t E l d l ti i t
on this data type. Example declarations are: int age, score;
long int bignumber;
 2. Real Data Type(in C are float or double): numeric value with
h l b d d i l t 23 75 230000 2 3E5 i
whole number and decimal parts, e.g., 23.75, 230000 or 2.3E5 in
Scientific notation. Arithmetic operations are performed on this
data type. E.g.,
float salary;
float salary;
double bigrealnumber;

D t T
Data Types
3 Ch t D t T ( ll d h i C) ll l tt
 3. Character Data Type(called char in C): all letters,
numbers and special symbols (surrounded by single
quotation signs), e.g., ‘A’, ‘a’, ‘1’, ‘+’. E.g.,
h d l ti ‘A’
char grade, location=‘A’;
 4. String Data Type(implemented as char
variablename[ ] in C)
• Combination of more than one character
(surrounded by double quotation signs), e.g.,
“Randy”, “85611”, “519-111-2345”. Eg
Randy , 85611 , 519 111 2345 . Eg
declarations:
char lastname[15], address[30];

D t T
Data Types
 5. Boolean or LOGICAL Data Type (implemented with
int in C)
• TRUE or FALSE are the only data values.
TRUE or FALSE are the only data values.
• In C, an int variable with a value of 0 can be treated
as logical type FALSE, while a value of not equal to
0 (like 1 or a number > 1) is TRUE. E.g.,
int flag=0; /* declares flag as FALSE */
 Each data type has a data set the set of values from
 Each data type has a data set, the set of values from
which any datum of that data type is specified.

Data Types
Data Types
Data Type Data Set Example Data
I t (i t) All h l b 1999 67
Integer(int) All whole numbers, e.g.,
-231
to (231
-1)
1999, -67
Real (float/ All real numbers (whole 1999.0,
double) + decimal parts) 258923.61
0.00581
Character All letters, numbers, and ‘A’,`b’,`K’,
C a acte
(char)
ette s, u be s, a d
special symbols.
, b , ,
`1’,`8’,`+’
String(char
variable[ ])
Combination of >1 chars. “Atlas”,“956”
variable[ ])
Logical
(int with 0
!0)
TRUE FALSE TRUE FALSE
or !0)

O ti Ch t /St i D t
Operations on Character/String Data
1 Ch t /St i d t b d d
 1. Character/String data can be compared and
arranged in alphabetical order (using their ASCII codes)
• A comparison between characters ‘A’ and ‘B’ gives
‘A’ < ‘B’ since 65 < 66 (see Appendix A of text)
• The character string “Money” is greater than
“Make” because `o’=111 > `a’=97 but > is not used
Make because o 111 a 97 but is not used
for string comparison in C. String functions and
processing are discussed in ch. 8.
 2 Other character and string operations including a lot
 2. Other character and string operations including a lot
of built-in functions are available in C and more details
are in sections 4.3 and 8.4 of text.

U f Diff t D t T
Uses for Different Data Types
1 N i l D t (i t (i t/l i t) d
 1. Numerical Data (integer(int/long int) and
real(float/double))
• used in business, government & academic
applications for values such as salary, price, scores
• used for numbers that will require some
computations on them
computations on them
• E.g., number of employees, assignment marks,
salary.
2 Ch t D t ( h )
 2. Character Data (char)
• used for initials, grades or things needing only one
character. No mathematical calculation allowed.

U f Diff t D t T
Uses for Different Data Types
 3. String (char variablename[ ])
• used for names, labels and things needing more than
one character and not needing any mathematical
one character and not needing any mathematical
calculation
• e.g., student number, phone number & account
number.
 4. Boolean (int with value 0 or !0)
• used in making yes or no decisions
• used in making yes-or-no decisions
• e.g., is a student’s grade ‘A’ ?

R l f D t T
Rules for Data Types
1 D t t t ll i d E h t
 1. Data types are not usually mixed. E.g., character
data cannot be placed in a variable memory location
designated as numerical. C allows use of cast operator
f t i h
for type conversion when necessary.
 2. Data defining the value of a variable or a constant
will be one of four data types: numerical, character,
y
string and Boolean.
 3. The use of any data outside the data set of the data
type results in an error.
type results in an error.
 4. Only valid operations on a data type are allowed.
E.g., numbers designated as string type cannot be used
in calculations
in calculations.

Al ith i St t
Algorithmic Structure
 [Gl b l I t/O t t V i bl ]
 [Global Input/Output Variables]
[Function Prototype list : type and parameters]
Mainalgorithm
{
Input: Variables/ Constants lists and their types
Output: Variables lists and their types
Others: Variables/Constants lists and their types
/* Now the body of Main Driver or Control Module is defined*/
Instruction 1;
Instruction 2;
:
Instruction n;
}
[function definition 1] …
[function definition n]

C P St t
C Program Structure
[Optional Global Variable declarations]
[Function Prototype list : type and parameters]
int main(void)
{
{
variable declarations;
/* Now the body of Main Driver or Control Module is defined*/
Instruction 1;
Instruction 2;
:
Instruction n;
return 0;
}
[function definition 1] …
[f ti d fi iti ]
[function definition n]

T f Al ith i I t ti
Types of Algorithmic Instructions
A l ith i i t ti b f th f ll i
 An algorithmic or program instruction can be one of the following
types:
• 1. Read (scanf in C) or Print (printf in C) instruction - Read
instruction is used to read data from the key board while a
instruction is used to read data from the key board while a
Print instruction prints output to the monitor.E.g.,
Algorithm: Read (Num1);
Print (Num1);
C P f(“%d” &N 1)
C Program: scanf(“%d”, &Num1);
printf(“%d”, Num1);
• 2. Assignment instruction - used to copy a computed value on
the right hand side of an equation to the memory cell labeled
the right hand side of an equation to the memory cell labeled
the left hand side of the equation. E.g., both algorithm and
program: sum = Num1 + Num2;

T f Al ith i I t ti
Types of Algorithmic Instructions
3 A f ti ll d t d l t ti f
• 3. A function call - used to delegate some portion of
the task to a small independent program segment.
E.g., In both algorithm and program:
C t P d t(N 1 N 2 & d t)
Compute_Product(Num1, Num2,&product);
• 4. A Decision instruction - used to decide between
which one of a number of alternative instructions to
execute. E.g., if ((large % small) ==0) lcd = small;
• 5. A Repetition instruction - used to cause a
sequence of instructions to be executed repetitively a
sequence of instructions to be executed repetitively a
number of times or until some event occurs. E.g,
while, do-while and for instructions.

Read(scanf) and Print(printf)
I t ti
Instructions
R d ( f) i t ti t i t d t t d b th f th
 Read (scanf) instructions get input data typed by the user from the
key board, while print (printf) instructions display the value of a
variable or an expression on the screen.
 The general forms of these two instructions are:
 The general forms of these two instructions are:
In an Algorithm:
Read(variable1, variable2,…, variablen);
Print(variable1, variable2, …, variablen);
 The format of C program scanf and printf
instructions are:
 scanf(“format specifiers”, &variable1, &variable2, ..
& i bl )
,&variablen);
 printf(“format specifiers”, variable1, variable2, ..
,variablen);

I t ti
Instructions
 Both scanf and printf accept a number of parameters
 Both scanf and printf accept a number of parameters
(arguments).
 A parameter could be a variable name, an expression
or a string literal, but only variable name parameters
are accepted by scanf.
 Both scanf and printf have the first parameter as a
 Both scanf and printf have the first parameter as a
string literal for format specifiers (specifying the data
type of the variables or data in the parameters).
 Format specifiers for int is %d and %ld for long int,
%f for float and %lf for double, %c for char and %s
for string.
for string.

I t ti
Instructions
 Example 3.5: Find the sum of two numbers
Algorithm: Read (num1, num2);
Print (“The sum of”, num1, “and”, num2, “is”, sum);
Print ( The sum of , num1, and , num2, is , sum);
 C Program:
scanf(“%d %d”, &num1, &num2);
printf(“The sum of %d and %d is %d”, num1, num2,
sum);
 Note that if the variable type for scanf is string then
 Note that if the variable type for scanf is string, then,
the address operator, &, does not precede the variable.

O t t F tti ith i tf
Output Formatting with printf
U h f ifi %E % di l fl i i
 Use the format specifier %E or %e to display a floating point
number in exponential form, %o to display in octal, %x or %X to
display in hexadecimal. E.g.,
printf (“%en” pi*10); will print 3 14159e01
printf ( %en , pi*10); will print 3.14159e01.
 Specify the number of columns, “c”, used to print an integer value
with specifier %cd, e.g., %3d, %4d. E.g.
printf (“%3dn” 25);
printf ( %3dn , 25);
printf (“%4dn”, 25);
 The number of columns, “c”, and number of digits, “d”, to the
i ht f d i l i t f fl ti i t l i ifi d ith
right of decimal point for a floating point value is specified with
%c.df, e.g., %8.1f.
printf (“%8.1fn”, 3.14159);

O t t F tti ith i tf
Output Formatting with printf
 An escape sequence is used for printing characters not
printable through simple inclusion in printf control
string. E.g., (“ printed as ``, newline printed as n) for
g g , ( p , p )
printf is represented by a backslash followed by a
particular escape character. See Table 3.6 for details.
Oth h t lik % t b t d t i t b
 Other characters like % must be typed twice to be
printed with printf as in printf(“ 50%%n”);
 Check tables 3.3 to 3.6 for format control string
g
parameters.

A i t I t ti
Assignment Instructions
A i i i i d d l f
 An assignment instruction is used to read a value from a memory
cell (any variable on its right hand side) and to assign a value to a
memory cell (the only variable on its left hand side).
Th l f f i t i t ti (i b th l ith
 The general form of an assignment instruction (in both algorithm
and C program) is:
variable = expression;
E l 3 6 C th t t f i bl 1 t 2
 Example 3.6: Copy the contents of variable assn1 to assn2.
 Solution: assn2 = assn1;
 Example 3.7: Copy the sum of assn1 and assn2 into assn3
 Solution: assn3 = assn1 + assn2;

E i
Expressions
Wh t i i ?
 What is an expression?
 An expression is a variable, a constant or a literal or a
combination of these connected by appropriate
operators. There are 3 basic types namely:
• Arithmetic expressions : variables are numerical
and connected by arithmetic operators (+,-,/,%,*)
and connected by arithmetic operators ( , ,/,%, )
• Relational expressions : variables are any type (but
same type on both sides of operator) connected by
relational operators (< > <= >= == !=) Result is boolean
relational operators (<,>,<=,>=,==,!=). Result is boolean
• Logical expression: apply to logical values using logical
operators NOT (!), AND (&&), OR (||).

O t
Operators
O ll h h d
 Operators tell the computer how to process data
 They are used to connect data (operands) in expressions and
equations to produce a result.
 Types of Operators
• 1. Arithmetic: addition (+), subtraction (-), multiplication (*),
division (/), integer division (/), modulos division (or remainder
after integer division %).
• E.g. if Jane has worked 17 days during the month in a 5-day
work week, how many whole weeks has she worked and how
many days not belonging to a week has she worked?
Numweek = TotalDays / 5;
Numdays = TotalDays % 5;
y y ;

O t
Operators
• 2. Relational Operators: <, >, <=, >=, == and !=
• Used to program decisions and need data operands
of any type except the two operands must be same
of any type except the two operands must be same
type.
• E.g., 31 > 15 is TRUE
• “Alpha” < “Beta” is wrong operation in C because
string comparison is done with function (strcmp).
• ‘C’ < ‘A’ is FALSE
• ‘C’ < ‘A’ is FALSE
• Results of these operators are either TRUE (!0) or
FALSE (0)
( )

O t
Operators
• 3. Logical Operators: Used to connect relational
expressions (decision-making expressions)
• Logical operators are NOT (!), AND (&&), OR (||)
Logical operators are NOT (!), AND (&&), OR (||)
• E.g., Refuse registration into 60-141 if mark in 60-
140 is less than 50%.
• if (m60140 < 50)
printf (“Error, Need at least a 50%% in 60-140”)
else
else
printf(“Registration in 60-141 successfuln”);
• Operands and results are logical type (TRUE or FALSE)

D fi iti f L i l O t
Definition of Logical Operators
 NOT (!)
A ! A
T F
F T
AND (&&)
A B A && B
T T T
T F F
F T T F F
F T F
F F F
OR (||)
OR (||)
A B A || B
T T T
T F T
F T T
F F F

Precedence Hierarchy of Basic
O t i C
Operators in C
Hi O A i i i R l
 Higest Operator Associativity Rule
( ) left to right
Functions left to right
!, (-) right to left
*, /, % left to right
+, - left to right
<, >, <=, >=, left to right
==, != left to right
&& left to right
g
Lowest || left to right
 Parenthesis can be used to overide precedence order

S tti N i l E i
Setting up Numerical Expression
 1. Set up the following mathematical expression for use
in a C program.
 a. X(3Y + 4) - 4Y
 a. X(3Y + 4) 4Y
X + 6
 Ans:
 b. Set up the following math equation as a C equation.
 Y + 3 = X (Z + 5)
A
 Ans:

S tti U R l ti l E i
Setting Up Relational Expression
 1. Given the expression X is less than Y + 5, set it up for
use in a C program.
 Ans:
 Ans:
 2. In order to cash a check, a customer must have a
driver’s license (A) or a check-cashing card (B) on file
at the store, set up this transaction for a C program.
 Ans:

E l ti M th ti l E i
Evaluating a Mathematical Expression
 Evaluating a math expression means assigning values
to all variables and testing the result to determine if it
is correct.
 Evaluate
 5 * (X + Y) - 4 * Y / (Z + 6)
with X = 2, Y=3, and Z=6

Evaluating Relational/Logical
E i
Expressions
 Evaluate the Relational Expression
A - 2 > B
where A=6, B= 8
,

 Evaluate the logical Expression
g p
A && B || C && A
with A=TRUE, B=FALSE, C= TRUE

Evaluating a Relational/Logical
E i / i t i t ti
Expressions/assignment instructions

E l t th f ll i i t i t ti
 Evaluate the following assignment instruction
Q = !(A < B) && (C || D)
where A=4, B=2, C=TRUE and D=FALSE

Oth C O t
Other C Operators
1 C’ I t O t (++) f ddi 1 t
 1. C’s Increment Operator (++) for adding 1 to a
variable.
E.g., Num=Num + 1; is same as :
N ++ ( tfi f th t dd 1 ft i N )
Num++; (postfix form that adds 1 after using Num)
and
++Num; (prefix form that adds 1 before using Num)
Num; (prefix form that adds 1 before using Num)
 2. C’s Decrement Operator (--) for subtracting 1 from a
variable.
E N N 1 i
E.g., Num = Num – 1; is same as:
Num--;
and --Num;

Oth C O t
Other C Operators
 3. Bit Operations in C
• A) Bitwise OR (|) for ORing two bit values.E.g.,
1 | 0 is 1, 1 | 1 is 1 and 0 | 0 is 0
1 | 0 is 1, 1 | 1 is 1 and 0 | 0 is 0
• B) Bitwise AND (&) for ANDing two bit values. E.g.,
001111 & 010111 is 000111
• C) Bitwise Exclusive OR (^) that returns 1 only
when one of the two input bits is 1. E.g., 1 ^ 1 = 0, 0
^ 0 = 0 and 1 ^ 0 = 1 0 ^ 1 = 1
0 0 and 1 0 1, 0 1 1.
• D) Bitwise Inverse operation (~), which flips the
value of an input bit. E.g., ~ 1 is 0 and ~0 is 1.

Oth C O t
Other C Operators
E) Bit i l ft Shift ti (<<) f hifti th i t l
• E) Bitwise left Shift operation (<<) for shifting the input value
a number of bits to the left. E.g.,
00010101 << 2 is 01010100
• F) Bitwise Right shift operation (>>) for shifting the input
F) Bitwise Right shift operation (>>) for shifting the input
value a number of bits to the right. E.g.,
00010101 >> 2 is 00000101
 4. C’s sizeof operator, which returns the number of
C p ,
bytes a variable of type requires. E.g., sizeof(int) is 4.
 5. C’s cast operator, which accepts an expression as its
operand and converts the type of the operand to the
operand and converts the type of the operand to the
type specified by the cast operator. Used as:
(Type) Expression

Oth C O t
Other C Operators
6 C’ O t A i O ti U d f iti
 6. C’s Operator Assign Operations: Used for writing
short forms of various forms of assignment
instructions. These instructions have an arithmetic (+, -
* / %) bit i ( ^ | &) t
, *, /, %) or bitwise (<<, >>, ^, ~, |, &) operator
preceding an assignment operator. General form is:
 Variable operator= value;
E.g., total += 40 means total = total + 40;
total -= 10 means total = total – 10;
total /= 4 means total = total / 4;
 Figure 3.4 of text shows the comprehensive operator
precedence and association order in C.

4. Problem Solving Tools (Top-Down
D i )
Design)
 Objective: 1. Discuss structure chart
• 2. Discuss functions and algorithms with
parameters, local and global variables
parameters, local and global variables
• 3. Discuss Built-in Functions and flowcharts.
 Top-down design approach to problem solving is based
g g
on the principle of “divide and conquer”.
 It breaks down the problem to be solved into smaller
sub problems using the problem solving tool of
sub-problems using the problem solving tool of
structure chart

Th St t Ch t
The Structure Chart
 Example 4.1: Write a solution (algorithm/program)
that inputs three different integers from the keyboard
and then prints the sum, average and product of these
p , g p
numbers. Use top-down design approach showing all 6
problem solving steps.
T d d i h t t h t ith
 Top-down design approach uses a structure chart with
the main problem as the control module and the
subtasks located below it.
 A module processes only those tasks directly below and
connected to it.

Th St t Ch t
The Structure Chart
 Modules are given unique number labels based on their
level with the top labeled 0000
Control
0000
FindSum
2000
FindProd
3000
FindAve
4000
ReadData
1000
PrintResult
5000

T f M d l i P bl
Types of Modules in a Problem
 1 Control Module or the Main Driver: shows the
 1. Control Module or the Main Driver: shows the
overall flow of the problem and calls other modules
 2. Init Module - for initializing data; e.g., Sum=0, knt=1
3 R d d D t V lid ti M d l
 3. Read and Data Validation Module
 4. Calculation Modules: for arithmetic calculation,
string manipulations like sorting
 5. File Maintenance Modules for adding or deleting
records from a file
 6. Print Modules: Prints outputs
 7. Wrap-Up Module: E.g. closing files or printing to
mark normal end of program.

C h i d C li
Cohesion and Coupling
 In separating a problem into parts it is desirable to
 In separating a problem into parts, it is desirable to
• 1. Create modules that perform independent
functions with one entrance and one exit -- cohesion
– Cohesion allows modules to perform independent
tasks (e.g., functions FindSum, FindDiff)
• 2. But modules need to work together towards
solving the bigger problem --- Coupling
– Coupling allows connecting modules through an
Coupling allows connecting modules through an
interface where data can be transferred from one
module to another (e.g., through parameters and
l b l i bl )
global variables)

C li T h i
Coupling Techniques
Th t i h d t b i t d b t
 That is, how can data be communicated between
modules? (3 approaches)
• 1. Use of Parameters in functions, e.g.,
– a) Call-by-Value Parameters with a function
return value for the function output. An example
call is Sum = FindSum(X,Y)
call is Sum FindSum(X,Y)
– b) Call-by-Reference Parameters for function
outputs. Example call is FINDSUM(X,Y,&Z)
2 U f D t th t ll d l ( l b l
• 2. Use of Data that all modules can access (global
variables)

i C i C i
Top-Down Design: Cohesion and Coupling
 Top-Down design is achieved through cohesion
(separating a large problem into independent modules)
and coupling (modules working together towards one
p g ( g g
goal).

Ad t f T D D i
Advantages of Top-Down Design
 1. Many programmers can work on a large problem
producing faster results
 2. It is much easier to write and test many small
 2. It is much easier to write and test many small
modules than a single one
 3. It is much easier to modify small modules.
 4. Reusability: a defined module can be used several
times by any module.

F ti
Functions
A f ti i t f i t ti th t f ifi
 A function is a set of instructions that performs specific
tasks and can return only one value although it can
modify others through parameters (call-by-reference).
 Functions contribute towards the solution of a problem
 They mostly make the solution of a big problem more
efficient because they can be reused, more elegant
efficient because they can be reused, more elegant
because it is structured and easier to read
 Many languages provide a variety of built-in functions.
H d l f th t t h t d fi d
 However, modules of the structure chart are defined as
functions in the problem solution by the problem
solver.

F ti
Functions
A f i d b id d f h d l i h
 A function needs to be provided for each module in the structure
chart.
 In the solution, we first provide each function prototype used to
t ll th il f ti t t th t f lt th t
tell the compiler functions to expect, the type of result they return
and their parameter types
 Secondly, we provide the full algorithmic/program definition of
h f ti
each function
 Format for specifying a function prototype is
functiontype functionname (type for par1, type for par2, …, type
f )
for parn);
 Example function prototype: int FindSum(int, int, int *);
 Example funtion header: int FindSum(int X, int Y, int *Sum);

F ti D fi iti St t
Functions Definition Structure
 Functiontype Functionname ([type par1], ..[type parn])
{
[local variable declaration];
[ ];
instruction1;
instruction2;
:
instructionn;
[return (output variable or expression or 0)];
}

F ti D fi iti E l
Functions Definition Example
 int FindSum(int first, int second)
{
int sum; /* This is a local variable of FindSum */
;
sum = first + second;
return(sum);
return(sum);
}

F ti P t
Function Parameters
 Parameters are data needed by the functions to return
results
 E.g., in X = SQRT(N), N is the parameter, and in
 E.g., in X SQRT(N), N is the parameter, and in
Getsum(X,Y,&Z), X,Y,&Z are the parameters.
 Parameters are surrounded by parenthesis
 A function can have 0 or more parameters
 E.g., rand( ) generates a random number
A b i bl
 A parameter can be a constant, variable or an expression
 E.g. valid call is: Getsum(29, 10, &Z)

P t
Parameters
 Parameters are data passed from one module
(function) to another.
 They enable us to avoid using global variables so that
 They enable us to avoid using global variables so that
we can improve on data protection.
 Parameters are enclosed in brackets in the definition of
the module (these are called formal parameters).
 Any other module can request the services of this
module by specifying the actual value for each
module by specifying the actual value for each
parameter in the exact order they appear in the
definition and with same data type.

P t
Parameters
 Parameters used in the calling statements are called
 Parameters used in the calling statements are called
actual parameters.
 The formal list and the actual list do not need to have
the same name so long as they are in the correct order
with the right data type.
 Parameters can be passed in two ways
 Parameters can be passed in two ways
• 1. Call-by-Value: Here, only the value of the variable
specified in the actual parameter list is passed to the
module called (not its address).
• means value the actual parameter had in the calling
module is not overwritten
module is not overwritten.

P t
Parameters
• 2. Call-by-reference Parameter: The address of the
memory location for the actual parameter is passed
to the called module. Example in the function call,
p ,
FindSum(X, Y, &Sum), the actual parameter &Sum
is the address of the Sum in the calling module.
S th l it h i th lli d l b f th
• So, the value it has in the calling module before the
call can be changed or replaced.

Address Operator (&), Pointer
V i bl d I di ti O t (*)
Variable and Indirection Operator (*)
 A pointer variable stores only memory addresses
 A pointer variable has to be declared before use in a
program with the format:
program with the format:
datatype_pointed_to *variablename;
E.g., if in main, Num1 is an integer variable with value 35
g g
and Sum is another int variable with value 200.
 We might want to call a function to find the sum of
Num1 and Sum with the call FindSum(Num1 &Sum)
Num1 and Sum with the call FindSum(Num1, &Sum).
 The actual parameter &Sum is the address of the
variable Sum. This means that in the definition of

Address Operator (&), Pointer
V i bl d I di ti O t (*)
Variable and Indirection Operator (*)
th f ti Fi dS th d f l t h t b
 the function FindSum, the second formal parameter has to be
declared as a pointer variable that points to an integer value.
Thus, the Function header is:
 void FindSum(int Num1, int *Sumf)
 void FindSum(int Num1, int Sumf)
 Here, the formal parameter Sumf, is a pointer variable.
 Note that in the function call, FindSum(Num1, &Sum), the address
operator (&) is used to obtain the address of the variable Sum in
operator (&) is used to obtain the address of the variable Sum in
main.
 The indirection operator (*) is used to obtain the value pointed to
by the pointer variable using the pointer variable name. E.g., to
add and print the sum in main using the Sumf in the function
FindSum, we use:
 *Sumf += Num1;
printf (“%d” *Sumf);
printf ( %d , *Sumf);

P t E l (E l 4 2)
Parameter Example (Example 4.2)
 Given the following program solution, show the values of the variables a, b,
g p g
c, x, y, z in the control module (module1) after each function call to
module2.
 /* function prototype declaration for Module2 */
void module2(int int int *);
void module2(int, int, int *);
void main(void) {
int a=3, b=4, c=5, x=7, y=8, z=10;
/* body of main */
/ y /
module2 (a, b, &c); /* a first call to Module2 */
module2 (x, y, &z); /* a second call to Module2 */
}
void module2 (int a, int b, int *c)
{ a += 4;
b += 4;
*c += 4; }

P t E l
Parameter Example

Th Al ith /P
The Algorithms/Programs
 Algorithms are mostly written in Pseudocode (a cross
between English language and high level programming
language)
g g )
 Each instruction in an algorithm should directly
convert to a programming language statement during
di
coding.
 Each module in the structure chart has a separate set
of instructions in the algorithm defined as a function.
g

Al ith E l (E l 4 3)
Algorithm Example (Example 4.3)
 Provide the algorithm and program to Example 4.1
using the structure chart already defined and
parameters. Also provide the flowchart solution.
p p

Fl h t
Flowchart
 The solution to a problem can be organized in a
number of ways and each algorithmic solution
corresponds to a flowchart.
p
 A flowchart is a graphical representation of an
algorithm. It shows the sequence of execution of the
i t ti
instructions.
 Flowchart and algorithm represent the same execution
flow in different forms.
 A flowchart always starts at the top of the page with
straight and neat connecting flow lines.

Fl h t
Flowchart
 Flowchart symbols are given below:
Start, End, Exit
Return, enter
Automatic counter
for (knt = s; knt
knt
s (relop)e
Module
Decision, while,
it h
relop e; knt arithop=
i)
( p)
(arithop)i
On-Page Connectors
switch
Read, Print
g
Off-Page Connectors
Assignment instr. Flow lines
Indicating function parameters
g p

L l d Gl b l V i bl
Local and Global Variables
 Cohesion and Coupling are realized through the concept
 Cohesion and Coupling are realized through the concept
of local and global variables
 In a module, the difference between local and global
variables is in their scope (where in which modules their
variables is in their scope (where, in which modules their
values are allowed to be used)
 Local variables can be used only inside the module they
d l d
are declared.
 Global variables are declared outside functions and can
be used by only functions below their declarations in the
y y
algorithm or program.
 Global variable is one coupling method, a better
coupling method is use of parameters
coupling method is use of parameters

L l d Gl b l V i bl
 Example 4.4: Solve the problem of Example 4.1 using
global variables and not parameter passing. Show all
the local and global variables in your solution.
g y

L l d Gl b l V i bl

Sh tf ll f Gl b l V i bl
Shortfalls of Global Variables
 1. Side Effects: A global variable may be accidentally
or wrongly altered by an incorrect or malicious module
(that is, no protection of data)
( , p )
 2. No Duplication of Variable names: When an inner
module declares a local variable with same name as the
l b l i bl ll h it k t thi i bl i
global variable, all changes it makes to this variable is
local and it no longer has access to the global variable.

B ilt i F ti
Built-in Functions
 Some common built-in functions provided by C
language are:
 1. Mathematical functions: E.g., sqrt(x), exp(x), log(x), ceil(x), floor
g , q ( ), p( ), g( ), ( ),
(x), pow(x,y), fabs(x) for absolute value
 2. String Functions:E.g., copy part of the string into another
variable, find number of characters in a string. E.g.,
, g g ,
strcmp(s1,s2), strstr(s1,s2), strcpy(s1,s2), strlen(s), strcat(s1,s2)
 3. Character Functions: For manipulating character data. E.g.,
isdigit(C), islower(C) for seeing if C is lower case letter or not.
g ( ), ( ) g
 4. Conversion Functions: convert data from one data type to
another. E.g., used to convert a string value to a numerical value,
in “C lang.” atoi(“2593”)=2593 (integer value)
g ( ) ( g )

B ilt i F ti
Built-in Functions
 5. Utility Functions: used to access information outside
the program and the language in the computer system,
e.g., date and time functions.
g ,

5 P L i St t
5. Program Logic Structures
Obj ti
 Objectives
 1. Program Logic structures (General)
 2. Discuss Sequential logic structure
. scuss Seque t a og c st uctu e
 3. Discuss solution testing and documentation
 The logic structure of a program enforces the sequence
f ti f i t ti i th d th
of execution of instructions in the program and the
main logic structures are:
• sequential logic structure and function calls
• Decision logic structure and
• Repetition logic structure

P L i St t
Program Logic Structures
 Thus, to provide a good solution to any problem, we
, p g y p ,
should proceed as follows:
 1. Use top-down design approach when necessary.
 2. For defining both the control module and the
functions in the solution, use the relevant structure(s)
among the three program logic structures:
a o g t e t ee p og a og c st uctu es:
• a. Sequential structure (executing instructions. one after the
other)
• b Decision Structure (executes one of many alternative
• b. Decision Structure (executes one of many alternative
instructions.)
• c. `Repetition Structure (executes a set of instructions. many
times
times

P L i St t
Program Logic Structures
 3. Eliminate duplication of steps in parts of same
program by using a module that can be re-used
 4. Improve readability using proper naming of
 4. Improve readability using proper naming of
variables, internal documentation and proper
indentation.

Problem Solving with Sequential
L i St t
Logic Structure
 Sequential logic structure is the most common and
simplest structure
 Sequential structure asks the computer to process a set
 Sequential structure asks the computer to process a set
of instructions in sequence from top to the bottom of an
algorithm.

L i St t
Logic Structure
Thi i th d f lt t t d ll bl thi t t i
 This is the default structure and all problems use this structure in
possible combination with other structures
int main (void) t t
int main (void)
{
Input variable list ;
Output variable list;
start
instr. 1
instr 2
p ;
Instruction 1;
Instruction 2;
:
Instruction n;
instr. 2
instr. n
End
;
return 0;
}
 Execution flow is Instruction1, followed by 2, 3, 4, etc.

T ti th S l ti
Testing the Solution
 Testing the algorithm or program entails selecting test
data to check the correctness of the algorithm/program.
 With the test data stepping through the program
 With the test data, stepping through the program
should give the expected results
 Test data should be selected to test all possible
p
situations that may arise (e.g. -ve, 0, +ve)
 Program testing entails pre-computation of correct
result first followed by hand simulation or tracing of
result first, followed by hand simulation or tracing of
the program to obtain the result produced by the
program, which should be the same as the correct result.

I t l d E t l D t ti
Internal and External Documentation
 Internal documentation are remarks written with the
instructions to explain what is being done in the
program
p g
 External documentation are manuals written for the
user to know how to use the program
 Objective of internal documentation is to make
program easily readable, maintainable and expandable
by either the original programmer or another
y g p g
programmer.
 It includes
• the input, output and processing information

I t l d E t l D t ti
Internal and External Documentation
V i bl it f th d
• Variable usage, writer of the program and
• other acknowledgements
 Objective of External documentation is to make
Object ve o te a docu e tat o s to a e
program easy to use.
 In solving problems, experienced problem-solvers use
the sequence of steps:
the sequence of steps:
• 1. The Structure Chart
• 2. The Algorithm or the flowchart and/or
• 3. The program.
 Thus, a problem solver can go straight to step 3 or get to step 3
through step 1, or through both steps 1 and 2. Ultimate solution is
g p g p
3 (the program).

L i St t
Logic Structure
Ch k E l 5 1 d 5 2 i th b k h i
 Check Examples 5.1 and 5.2 in the book showing
programs with only sequential logic instructions, use of
built-in functions, and selecting test data to evaluate all
ibl th f
possible paths of a program.
 Other important parts of program solution shown by
example 5.2 are use of internal documentation
(comments) for making programs readable and
maintainable as well as external documentation (e.g.,
user manual to specify how the program should be
p y p g
executed) and the type of input and output data it takes
and prints.

6 P bl S l i ith D i i
6. Problem Solving with Decisions
Obj ti
 Objectives
 1. Discussing Problem solution using both Sequential
and Decision logic structures.
• if/else and switch_case instructions
Th D i i L i St t h t i i t ti
 The Decision Logic Structure has two main instructions
- the if instruction and the switch_case instruction.
 The if/else instruction
 Meaning is IF the condition is true, we execute the TRUE part (a
set of instructions), else (that is, condition is false), we execute the
ELSE part (another set of instructions)

P bl S l i ith D i i
Problem Solving with Decisions
 if (condition(s))
{
TRUE instructions; }
else
{ FALSE instructions; }
A
A
IF
(cond)
FALSE TRUE
Instruction set
for FALSE
Instruction set
for TRUE
Decision
Structure

 Example 6.1: Write decision instruction to indicate if a
given integer number is an even number.
if ((Num%2) == 0)
printf(“ The number is an even numbern”);
l
else
printf(“ The number is an odd numbern”);

 Example 6.2: A retail store allows part-time workers a
rate of $8.00 an hour for a maximum of 20 hours of
work in a week. However, a part-time worker earns
, p
$10.00 an hour for each additional hour over 20 hours.
Write a decision instruction to compute a given part-
time worker’s wage for a week
time worker s wage for a week.

D i i L i (If I t ti )
Decision Logic (If Instructions)
 The if form
• Process all decisions sequentially one after the other
(no ELSE part of the instructions)
(no ELSE part of the instructions)
• if (condition1) (Draw the flowchart)
Instructions_T1;
• if (condition2)
Instructions_T2;

D i i E l
Decision Example
 Example 6.3: Solve the problem of Example 6.2 using
straight through if instructions (with no else part).
• Num hours Week wage
Num_hours Week_wage
hours <= 20 8 * hours
hours > 20 (8 * 20) + (10 * (hours-20)

D i i E l
Decision Example
 Comparing solution versions 6.2 (if with else part) and
6.3 (if with no else part) of the same problem, which is
more efficient and why?
y

if INSTRUCTION
if INSTRUCTION
N h i it ffi i t t th if f ( ith l
 Now, when is it efficient to use the if form (with no else
part) of the decision structure?
 With some problems where the sequence of tests are to
be conducted on different variables, the only solution is
the straight through if structure (with no else part).
 Example 6.4:
Example 6.4:
• Assume you want to assign a number of students
(S), to different classrooms for an exam such that
each room takes only 150 students and once you
each room takes only 150 students and once you
have got 150 students for one room you initialize S
back to 0. Similarly, the GA’s (G) for supervising

if/th INSTRUCTION
if/then INSTRUCTION
• the exams are assigned 10 to each room. Once you
have got 10 GA’s assigned, you initialize G back to
0. Write decision instructions for initializing both S
g
and G to 0.

N t d if/ l F
Nested if/else Form
 Nested if/else form is the if instruction where either the
“TRUE” sequence of instructions (first part) or the
“FALSE” sequence of instructions (“else” part), or
q ( p ),
both sequences contain another “if” instruction.

N t d if/ l F
Nested if/else Form
if (d i i i 1 i )
 if (decision expression 1 is true )
 if (decision expression for expression1-true is true)
 instructions for when expression of expression1-true is true;
l
 else
 instructions for when expression of expression1-true is false;
 else
if (d i i i f i 1 f l i )
 if (decision expression for expression1-false is true)
 instructions for when expression of expression1-false is true;
 else
 instructions for when expression of expression1-false is false;
 This structure has if instruction in both the True and else parts.

N t d if/ l F
Nested if/else Form
 Example 6.5:
• In a city, the monthly bus fare for seniors 65 years
or older is half the normal rate of $45.00 for adults
or older is half the normal rate of $45.00 for adults
while fare rate for kids under the age of 18 is
one_third the normal rate. Write an IF instruction
t d t i h t f t h i
to determine what fare to charge a person given
his/her age.
 Solution
• Conditions(Age) Actions(fare)
Age >= 65 1/2 * 45
65 > Age >= 18 45
18 >Age 1/3 * 45
18 >Age 1/3 45

N t d if/ l F
Nested if/else Form
 For problems involving nested if instructions in only
the Else or True part, they can be expressed in two
ways, namely:
y , y
• 1) Using positive logic, and
• 2) Using negative logic.
 Positive logic writes the instruction such that some
action (like assignment instruction) is executed if
decision expression evaluates to TRUE but another IF
decision expression evaluates to TRUE but another IF
instruction is executed when decision evaluates to
FALSE

U i P iti D i i L i
Using Positive Decision Logic
 if (Age >= 65) (Draw the flowchart)
Fare = (0.5) * 45.0;
else
if (Age >= 18)
Fare = 45.0;
else
else
Fare = 0.33 * 45.0;

U i N ti L i
Using Negative Logic
 Process a set of instructions when “if expression” evaluates to
Process a set of instructions when if expression evaluates to
FALSE but process another decision instruction when “if
expression” evaluates to TRUE.
 Can use negative logic to decrease the number of tests
Can use negative logic to decrease the number of tests
 The Age example with negative logic
 if (Age < 65) (Draw Flowchart)
if (Age < 18)
if (Age < 18)
Fare = (1/3) * 45.0;
else Fare = 45.0;
else
else
Fare = (1/2) * 45.0;

L i C i
Logic Conversion
 May help improve on efficiency or readability of a
solution
 E.g., a decision should always have instructions for the
 E.g., a decision should always have instructions for the
TRUE section but not necessarily for the FALSE
section.
 A solution with no instructions for the TRUE section is
better converted to negative logic.
 How? To convert from positive to negative logic do the
 How? To convert from positive to negative logic do the
following:

L i C i
Logic Conversion
1 W it th it f h l ti l t i
 1. Write the opposite of each relational operator in
every decision as:
• operator opposite
< >=
<= >
> <=
>= <
== !=
!= ==
 2. Interchange all the TRUE set of instrs. with the
corresponding ELSE set of instrs.

L i C i
Logic Conversion
 Example 6.6
• Calculate the number of bonus air miles earned
given that the bonus air miles earned by customers
given that the bonus air miles earned by customers
is 100 if traveled miles exceed 5000 in a period of
time, but 60 bonus air miles are earned if traveled
il l d 3000 hil 10 b i il
miles only exceed 3000 while 10 bonus air miles are
earned otherwise by the customer. Write two
positive logic if program/algorithmic solutions for
the above problem. Then, write 2 negative logic
solutions.

L i C i E l
Logic Conversion Example

Whi h if L i t Ch ?
Which if Logic to Choose?
 Choose the if logic that is most efficient, and most
readable
 Most efficient logic is characterized by
 Most efficient logic is characterized by
• 1. Fewer tests both when you know about data and
when you don’t
• 2. Easiest to maintain (modify)
 In the above example, solutions 1 and 2 (positive logic)
are most readable with same number of tests So any
are most readable with same number of tests. So, any
of the two may be chosen.

it h I t ti
switch_case Instruction
 The switch_case Instruction is the second type of
instruction with the decision logic structure.
• It is made up of several or more sets of instructions,
It is made up of several or more sets of instructions,
only one of which will be selected if a case label
matches the label for that set of instructions.
• switch_case instruction is used to decide which one
execution path among many to choose, while IF
instruction chooses one path out of two alternatives.
p
 Format of switch_case instruction is given below:

it h L i St t
switch_case Logic Structure
it h (EXPRESSION) {
 switch (EXPRESSION) {
case label1:instructions to execute if expression = labe11;
break;
l b l2
case label2: instructions to execute if expression = labe12;
break;
:
case labeln: instructions to execute if expression = labe1n;
case labeln: instructions to execute if expression = labe1n;
break;
[default: instructions to execute if expression
matches none of labels 1 to n above;
matches none of labels 1 to n above;
break;]
}

it h L i St t
A
A
switch
Instructions;
case label1 case label2
Instructions;
case labeln
Instructions;
default
(expr)
……...
Instructions;
break;
Instructions
break;
Instructions;
break;
Instructions;
break; ..
B
FLOWCHART Diagram for the switch_case Logic structure

it h L i St t
 Give the if instruction Equivalent to the switch_case
instruction.

it h I t ti E l
switch_case Instruction Example
 Example 6.7: Write a program that keeps track of the
number of houses in each of the five zones labeled A, C,
K, L, Q in a city. It reads the zone of a given house,
, , Q y g ,
increments the appropriate zone count and prints the
number of houses in each zone.

it h I t ti E l
switch_case Instruction Example

i h I t ti E l
swich_case Instruction Example

7 R titi L i St t
7. Repetition Logic Structure
Obj ti
 Objectives
 1. Use three types of Loop instructions in problem
solving (while, do-while, for instructions)
 2. Use nested loops in problem solutions touching on
recursion as well.
 The Repetition Logic Structure
 The Repetition Logic Structure
 Repetition logic structure allows a sequence of
instructions to be executed continuously as long as a
diti i ti fi d
condition is satisfied.
 E.g. loop problems: Counting, accumulating sum
 3 types of loop instructions are used:

hil I t ti
while Instruction
1 hil I t ti
 1. while Instruction
 Tells the computer to (a) test a <condition> and while
that condition is true (b) to repeat all instructions
between the while (begin) bracket “{“ and (end) “}”.
• Initialization instructions;
while (condition(s))
( ( ))
{
INSTRUCTION;
INSTRUCTION;
:
Update Instructions;
}

while Instruction
while Instruction
A
while loop chart A
A
Initializations
Initializations
while
(conds)
if
(conds)
F
F
T
Instructions
Instructions
Update Instr
T
B
Update Instr
B
Update Instr
goto
hile if i t ti i l t f hil
B
while if instruction equivalent of while

hil I t ti
while Instruction
 While loop can be used for both event-controlled and
counter-controlled loop
 Important parts of a loop structure are:
 Important parts of a loop structure are:
• 1. Initialization of variables (control and
accumulation variables)
E.g., count = 0; and Sum = 0
• 2. Testing of the control variables (for termination
condition) E g while (count < 10)
condition). E.g., while (count < 10)
• 3. Updating the control variable (to advance to next
data item). E.g., count ++

hil I t ti ( t t ll d)
while Instruction (counter controlled)
 Example 7.1: A class of ten students took a quiz. The
marks (integers in the range 0 to 100) for this quiz are
available to you. Determine the class average on the
y g
quiz using a program. [Complete this rough solution]
• 1. Declare Variables
• 2. Init_Module {Sum=0, Counter = 0}
• 3. while (Counter < 10)
{
{
– Read_Module(mark, sum)
– /*reads and adds to sum */

hil I t ti E l P bl
while Instruction Example Problem
– Counter = Counter + 1
– }
• 4 Finish Module /* does the following instrs */
• 4. Finish_Module /* does the following instrs. */
– average = sum/10
– Print Results Module (average)
Print_Results_Module (average)
• 5. } /* end of main program*/
 Note that the ReadModule and Finish_Module need to
be defined properly in a full program.

hil I t ti With S ti l
while Instruction With Sentinel
 Example 7.2: Write a program that counts the number
of houses belonging to each of the five zones A, C, K, L,
Q in a city. The zone of each house is entered for
Q y
reading and a sentinel value of ‘0’ is used to mark the
end of data.

hil I t ti E l P bl
while Instruction Example Problem

hil d EOF k
while and EOF marker
 Example 7.3: Write a program that counts the number
p p g
of houses belonging to each of the five zones A, C, K, L,
Q in a city. The zone of each house is entered for
reading and the last data line is marked with end of file
reading and the last data line is marked with end-of-file
marker.

hil d EOF k
while and EOF marker

(2) d hil
(2) do-while
T ll th t t t th t f i t ti
 Tells the computer to repeat the set of instructions
between the “do” and the “while” keywords as long as
the condition is TRUE.
 Differences between “do-while” and “while”
instructions
• 1. Test for loop termination condition is done at the
1. Test for loop termination condition is done at the
beginning with “while” loop but at the end with “do-
while” loop.
• 2 With the “do while” the loop must execute at
• 2. With the do-while , the loop must execute at
least once, with the “while” loop, zero iteration is
possible.

(2) d hil
(2) do-while
With “d hil ” l th l i t ti d t l t
 With “do-while” loop, the loop instructions are processed at least
once before the termination condition is tested.
 Thus, for problems that may need zero iterations (number of times
the loop is processed), “do-while” loop should not be used (E.g., no
the loop is processed), do while loop should not be used (E.g., no
data read)
 Format is:
• Initializations;
Initializations;
do {
Instruction;
Instruction;
:
update instruction
} while (CONDITION(S));

(2) do-while
(2) do while
A
A
do Instructions
Initializations
Initializations
Update Instr
Instructions
Update Instr
if
<conds>
goto
T
F
while
(conds)
T
B
REPEAT/UNTIL IF (DECISION) EQUIVALENT
F
( )
B
F
REPEAT/UNTIL IF (DECISION) EQUIVALENT

(2) d hil
(2) do-while
 Example 7.4: A computer class took a quiz. The scores
(integer in range 0 to 100) for this quiz are available to
you and the last data line is marked with a sentinel
y
value of -1. Determine class average using the do-while
loop structure.

d hil
do-while

(3) for Instruction (Automatic
C t L C t l)
Counter Loop Control)
 This “for” instruction decrements or increments the control variable each
 This “for” instruction decrements or increments the control variable each
time the loop is repeated
 e.g. for loop
 The initialization, termination value, testing and update of the control
variable all occur in the one loop instruction
variable all occur in the one loop instruction
 Format:
• for (counter = begin value; counter (relational_operator) end value;
• counter=counter (arithmetic operator) step)
• {
• instruction 1;
• instruction 2;
• :
• :
• instruction n;
• }

C t L C t l)
counter
Begin (relop)End
a) b)
Show the Decision Equivalent
for
g ( p)
(arithop) STEP
Instructions
a), b)
Instructions
Instruction
c)
COUNTER

C t L C t l)
 Example 7.5: A computer class of 15 students took a
quiz. The scores (integers in the range of 0 to 100) for
this quiz are available to you. Determine the class
q y
average on the quiz with a program.

C t L C t l)

N t d L & i di t
Nested Loops & indicators
 Nested loop instructions are loop instructions inside an
p p
outer loop
 Nested loops do not have to be same types of loop
t t
structures
 Event-controlled loops, programmed with while & do-
while loop structures make use of indicators.
w e oop st uctu es a e use o indicato s.
 Indicators are logical/control variables set inside a
program when a certain condition occurs (e.g., end-of-
fil d t i th fil lik
file or no more data in the file, or an error occurs like
invalid data)
 Indicators are also called flags, switches, dummy or trip values
g y p

E l P bl With N t d L
Example Problem With Nested Loop
 Example 7.6: Write a program and a flowchart that
utilizes nested looping to produce the following table of
values:
• A A+2 A+4 A+6
3 5 7 9
6 8 10 12
6 8 10 12
9 11 13 15
12 14 16 18
15 17 19 21

 Example 7.7: Write a program and a flowchart to
display the following checkerboard pattern
using nested looping.
g p g
* * * * * * * *
* * * * * * * *
* * * * * * * *
* * * * * * * *
* * * * * * * *

R i
Recursion
 Recursion is a type of loop structure where a module or
a function calls itself
 Some problems are naturally recursive, e.g., factorial
 Some problems are naturally recursive, e.g., factorial
 A recursive solution should have a base case for
termination
 Any problem that can be solved recursively can also be
solved iteratively
 Recursive approach carries more overhead in terms of
 Recursive approach carries more overhead in terms of
memory space needed during execution and processor
time.

R i
Recursion
 So, why use Recursion?
• For some problems that are naturally recursive,
providing and maintaining a recursive solution is
providing and maintaining a recursive solution is
easier
• In terms of performance, recursive solution takes
longer and consumes more memory
 Example 7.8: write a recursive program to obtain 10!

R i
Recursion

8 A
8. Arrays
 Objectives
 1. Develop problem solution using a more complex data
structure, arrays which will enable table look-ups,
structure, arrays which will enable table look ups,
sequential and others.
 2. Discuss string processing and functions.
 If we want to store 5 assignment marks for a student,
we can create the variables Asn1, Asn2, Asn3, Asn4,
Asn5
Asn5
 If there are 10 to 20 assignments to record, this
approach becomes clumsy

A
Arrays
 If we also have to record a matrix of 20 assignment
marks for say 100 students, with a different variable
for each assignment mark, we have:
g ,
Stu1_Asn1, Stu1_Asn2, ……., Stu1_Asn20
Stu2_Asn1, Stu2_Asn2,…….., Stu2_Asn20
: : : :
: : : :
Stu100_Asn1,Stu100_Asn2,….,Stu100_Asn20
 Approach is inconvenient and prone to error
 A way out? ---- Use ARRAY data structure

A
Arrays
A d t t t ll t th
 An array data structure allows us to use the same
variable name for the 20 assignment marks for one
student.
 Using an array, we replace Asn1, Asn2, ……,Asn20
with a single variable Asn subscripted as: Asn[1],
Asn[2], .., Asn[20].
 Thus, an array is a data structure allowing more than
one memory location to be designated for a single
variable.
variable.
 Each element of the array variable is referenced using
its subscript

A
Arrays
A f l f d t l f th
 Arrays are useful for many data values of the same
type, e.g., all ages, all grades etc.
 Arrays are easier to read and use in program
statements than having different variables.
 To use arrays in a program, they have to be declared
and the size of the array (number of elements) needs to
and the size of the array (number of elements) needs to
be included. Format is shown below:
 E.g., to declare a one-dimensional array in a program
datatype arrayname[size];
datatype arrayname[size];
e.g., int assn1[7];
 Two ways to declare the size or dimension of an array

A
Arrays
• 1. Static Arrays: allowed by many programming
languages.
– Size and dimension declared at the beginning and
Size and dimension declared at the beginning and
never changes during the execution of the
program
• 2. Dynamic Arrays: Number of array locations is a
variable which can be increased or reduced during
the execution of the solution (using malloc in C).
( g )
– More flexible but more time consuming during
program execution

A
Arrays
 The first array element (the base element) is numbered
zero (has subscript 0) in some languages like C, but
numbered 1 in some others.
 If the base element is 0, the second element is 1; and if
the base element is 1, the second element is 2.
A (b 0) A (b 1)
A[0] 0
A[1] 1
A[2] 2
A (base 0)
A[1] 1
A[2] 2
A[3] 3
A (base 1)
A[2] 2
: : :
A[n-1]
A[3] 3
: : :
A[n] N

A
Arrays
 By using the assignment instruction, we can assign the
value of a constant, a variable, or an expression to an
element.
 One Dimensional array is the simplest array structure.
Conceptually, a one dimensional array represents an
i bl th t h l l f l t
array variable that has only one column of elements.
 E.g. of a one dimensional array: 10 assignment marks
for student Maggie
gg

A
Arrays
 Example 8.1: Read and print the marks for 10
assignments obtained by student Maggie as well as her
average assignment marks.
g g

A
Arrays

A V i bl i F ti
Array Variables in Functions
 An array variable can be used any where any simple variable can
 An array variable can be used any where any simple variable can
be used in all types of instructions including function calls but a
complete array cannot be returned using a function return value.
 An array parameter passing all elements of the array, in a
f ti ll i l i l d th f th i bl
function call simply includes the name of the array variable
without specifying the dimension or size.
 However, an array’s dimension needs to be specified in the
function prototype and function header. Its size may also be
p yp y
specified if passed as a parameter in the function call.
 E.g., a function ReadData reads data into a 1-dimensional array of
seven assignment marks. The function prototype and header for
ReadData are respectively:
ReadData are respectively:
 void ReadData(int [], int);
 void ReadData(int assn [], int size)

A ( di i l ll l)
Arrays (one-dimensional parallel)
 Example 8.2: Write a program that computes the
assignment average for assignments 1 and 2 in a small
class of seven students whose names and ids are Maggie
gg
(id 1050), John (id 1051), Ken (id 1052), Joy (id 1053),
Pat (id 1054), Tim (id 1055) and Tom (id 1056). The
program reads their ids computes and prints the
program reads their ids, computes and prints the
average mark obtained by each student id as well as
asn1 and asn2 averages.

A ( di i l ll l)
Arrays (one-dimensional parallel)

A
Arrays
 Asn1[1] and Asn2[1] both relate to Student[1]; and
Asn1[5] and Asn2[5] both relate to Student[5]
 To declare these three arrays, we use
 To declare these three arrays, we use
int Student[7], Asn1[7], Asn2[7];

A E l
Array Example

A E l
Array Examples

A E l
Array Examples
 Example 8.3: We want to use arrays to summarize the
results of data collected in a survey. Forty students
were asked to rate the quantity of the food in the
q y
student cafeteria on a scale of 1 to 5 (1 means awful and
5 means excellent). Place the forty responses in an
integer array and summarize the results of the poll
integer array and summarize the results of the poll
using a C program.

A E l
Array Examples

T Di i l A
Two-Dimensional Arrays
Whil di i l h l b i t
 While a one-dimensional array has only one subscript
indicating the number of rows, a two-dimensional
array has two subscripts indicating
( b f b f l )
(number of rows, number of columns).
 A two dimensional array can be used to store a table of
values with more than one column (e.g., a Matrix).
g
 To declare a 2-dimensional array, use:
datatype arrayname[num_row][num_column];
Th t ll l f A 1[7] d A 2[7]
 The two parallel arrays for Asn1[7] and Asn2[7] we
defined earlier on, can be stored in one two dimensional
array as:(write answer here)

T Di i l A
E l 8 4 W i h h i
 Example 8.4: Write a program that computes the assignment
average for assignments 1 and 2 in a small class of seven students
named Maggie, John, Ken, Joy, Pat, Tim and Tom. The average
mark obtained by each student is also computed and printed
mark obtained by each student is also computed and printed.
Solve using two dimensional array where necessary.

T Di i l A

M ltidi i l A
Multidimensional Arrays
 These are arrays with three or more dimensions
 With three dimensional array, three subscripts are
needed and three nested loops are used.
needed and three nested loops are used.
 An example of a 3 dimensional array is given in the
course book section 8.2
 int Cube[row][column][depth];

St i P i
String Processing
A t i i C i f h t d l d
 A string in C is an array of characters declared as:
char variable[number of characters];
 The last character of the string is the null character ‘0’
 Thus a string with 20 characters has the 20th as ‘0’
 Thus, a string with 20 characters has the 20th as ‘0’
 E.g., char studentname[20] can hold only one student name with
up to 19 alphanumeric characters.
 Now if we want to declare a variable to hold 10 student names it
 Now, if we want to declare a variable to hold 10 student names, it
is declared as a 2-dimensional array:
char studentname[10][20];
 Names can also be initialized at declaration as:
 char studentname[10][20] = {“John Smith”, “John Adams”, “Mary
Goods”, “Peter Kent”, “Chu Lee”, “Paul Best”, “Okee Ndu”, “Pat
Madu”, “Andrew New”, “Mark Ogods”};

St i P i
String Processing
Lib f ti f t i i t d t t i l d
 Library functions for string input and output include:
 gets (stringvariable);
 fgets (stringvariable, length, filepointer);
t ( t i i bl ) f t ( t i i bl l th fil i t )
 puts (stringvariable); fputs(stringvariable, length, filepointer);
 sscanf(string_to_readfrom, format specifiers, variablelist);
 sprintf(string_to_printto, format specifiers, variablelist);
 Library functions for string copying, concatenation, comparisons
and others include:
 strcpy(s1, s2) , strncpy(s1, s2, numchars) , strcat(s1,s2) ,
strncat(s1 s2 n)
strncat(s1,s2,n) .
 The list of string functions in C library <stdlib.h> for I/O are
summarized in section 8.4, while functions for copying and other
operations are summarized in section 4.3 of book.
p

Searching or Table LooKup
T h i
Techniques
S hi i i li i f
 Searching is one important application of arrays.
 Searching entails using a value to look up another value in a table
of values. For example, 100 test scores are stored in an array
[100] d t t th ti di h th
score[100] and you want to answer the question regarding whether
there is any 96% in the 100 scores.
 You can go about this look-up in two ways
• 1. Sequential Searching
• 2. Binary searching
 Example 8.5: Given n test scores and a search key score, write a
p y ,
sequential search program to return the position of the first
element in the array equal to the key score.

S ti l S h
Sequential Search
 The program for sequential search is:
p g q
• int main (void) {
• int Score[10], key , k, I, n=10;
• scanf (“%d”, &key);
scanf ( %d , &key);
for (I = 0; I < n; I++)
scanf(“%d”, &score[I]);
• k = 0;
• while (key != score[k] && (k < n))
k = k + 1;
If (k>=n) printf (“element not found”);
else printf(“element %d is equal to key %d” k key);
else printf( element %d is equal to key %d , k, key);
return 0;
}

S ti l S h
Sequential Search
 Works well for small or unsorted arrays. Inefficient for
large arrays
 In the worst case, the algorithm will search through all
 In the worst case, the algorithm will search through all
n elements of the array before either finding the value
or not finding it at all
 In the best case, the algorithm searches through only 1
element

Bi S h
Binary Search
 Binary search is faster, but only works on sorted arrays
y , y y
as it eliminates half of the elements in the array being
searched during each iteration.
Bi h th id l t f i i
 Binary search compares the mid-element of remaining
array list to the search key.
• 1. Set the lower boundary at 0
. Set t e owe bou da y at 0
• 2. Upper boundary is set as the number of elements
in the array minus 1 (that is the last element)

Bi S h
Binary Search
• 3. The loop is started and will continue as long as
mid element if not the search key and the end of the
list is not yet passed. That is while ((test[mid] !=
key) && (LB <= UB)). If LB > UB, it indicates the
key) && (LB UB)). If LB UB, it indicates the
last element has been searched.
• 4. The mid-element number is calculated (truncated
to integer value) as mid = (LB+UB)/2
• 5. Also, upper and lower boundaries are re-
calculated. If search value is greater than value of
calculated. If search value is greater than value of
mid element number, then lower boundary is set to
one more than the midpoint, otherwise it is set to
l ( l ti 8 5 f d t il )
one less. (see solution 8.5 for details)

Bi S h
Binary Search
• 6. Once the search loop has ended, test to know
whether the search key was found or not. If the
lower boundary is greater than the upper boundary,
y g pp y,
it means element could not be found.

Bi S h Al ith
Binary Search Algorithm

Bi S h Al ith


Bi S h Al ith

Bi S h Al ith
 Example 8.6: Assume the following 10 test scores are
sorted in an array test[10], find if a score of 84 is in this
array using binary search.
y g y
Test(k) -56 63 65 71 72 75 80 81 84 86

S ti T h i
Sorting Techniques
 Sorting is the process of putting the data in
alphabetical or numerical order using a key field
 primary key is the first key by which data in a file is
 primary key is the first key by which data in a file is
sorted, e.g., area code for a mailing list
 Secondary key is the second key by which data in a file
is sorted within the primary key order.
 E.g., a mailing list sorted by area code can again be
sorted in alphabetical order of name within each area
sorted in alphabetical order of name within each area
code.

S ti T h i
Sorting Techniques
 Sorting techniques include
• 1. Selection Exchange Sort, bubble Sort, Quick Sort,
Shell Sort and Heap Sort
Shell Sort and Heap Sort
 Best sorting techniques are determined by the number
of comparisons and switches that take place for a file of
n records in a specific order.

Th S l ti E h S t
The Selection Exchange Sort
 To sort n records
 Maintain 2 sublists within n records
• 1 List of sorted part (S)
• 1. List of sorted part (S)
• 2. List of unsorted part (U)
 Initially number of elements in S=0 and number of
Initially number of elements in S 0 and number of
elements in U = n
 1. Find the smallest element in U and switch its position
i h h fi l f U
with the first element of U
[now number of elements in S=1 and number of
elements in U = n-1]
]

Th S l ti E h S t
2 Whil b f l t i (U) 1
 2. While number of elements in (U) > 1
• Find the smallest element U and switch with first
element of U. [Once switched this first element of U
becomes the last element of S]
 Example 8.7: sort the following in ascending order
using selection exchange sort
using selection exchange sort
 56
80
75
63
58
79

Th S l ti E h S t
 int main(void) {
int score[6], num_score, I, minpos, j, temp;
for (I=0; I < num score-1; I++)
( ; _ ; )
{
min = I;
for (j = (I+1); j < num score; j++)
for (j = (I+1); j < num_score; j++)
{
if (score[min] > score[j])
i j
min = j
} /* end of for j */

Th S l ti E h S t
if ( i ! I)
 if (min != I)
{
temp = score[I];
[I] [ i ]
score[I] = score[min];
score[min] = temp;
}
} /* f I */
} /* for I */
return 0;
} /* of main */

Th B bbl S t
The Bubble Sort
 Example 8.8: Sort in ascending order with bubble sort
 To obtain the S list from the U list, compare each
element in U with the next element and switch if
element in U with the next element and switch if
element is larger than next one
 56
80
80
75
63
58
58
79

Th B bbl S t Al ith
The Bubble Sort Algorithm
i t i ( id) {
int main (void) {
int score[6], numscore=6;
int temp, numleft ;
for (numleft=numscore-2; numleft >= 0; numleft- -)
for (numleft numscore 2; numleft > 0; numleft )
{
for (j = 0; j <= numleft; j++)
{
if (score[j] > score[j+1])
{ temp = score[j];
score[j] = score[j+1];
score[j+1] = temp; }
score[j+1] = temp; }
} /* end of for j */
} /* end of for numleft */
return 0;
return 0;
} /* end of main */

Th Q i kS t
The QuickSort
 Using Quicksort, sort
56 80 75 63 58 79

9 P i t Fil R d d th
9. Pointers, Files, Records and others
 Objectives
 1. Get introduced to more advanced data structures
like pointers, files, records, stacks, linked lists and
like pointers, files, records, stacks, linked lists and
binary trees
 Pointers
 A pointer is a variable that can store only memory
addresses as its value.

P i t
Pointers
Address labels memory
X John
Y 70.8
A 60
B *
C *
Here, cells X, Y and A hold ordinary data values while cells B and C hold
addresses of variables Y and A respectively.

P i t
Pointers
 A pointer variable needs to be declared before use and
the format for declaring them is:
 type of data it points to *pointervariable;
 type_of_data_it_points_to pointervariable;
 E.g, float *B;
 int *C;
 Operations on Pointer Variables
• 1. A pointer variable can be initialized to 0 or null
E B 0
E.g., B = 0;
meaning that it is pointing to nothing but it exists.

P i t
Pointers
 2. A pointer variable can be set to point to a variable by
assigning the address of the variable using address
operator (&).
p ( )
E.g. B = &Y;
C= &A;
3 W d it th d t l b i i t d t
 3. We can read or write the data value being pointed to
by a pointer variable through the pointer variable by
using the indirection or dereferencing operator (*).
E.g., print (*B) will display 70.8
*C = *C + 10 will replace the value in A with 70.

P i t
Pointers
 4. A pointer may be subtracted from another pointer
and a pointer may be incremented with an integer
value.
 5. A pointer can be assigned another pointer variable if
they both point to values of the same type.

Fil C t
File Concepts
S f h d d t f th k b d
 So far, we have read data from the key board
 If we write a program to process one thousand student
records, reading data from the key board, then, every
time we need to run the program again, we have to
start typing in all one thousand records.
 Approach in this case is inconvenient and prone to
Approach in this case is inconvenient and prone to
error.
 A solution to this problem is to pre-type our one
thousand records in a disk file save it and tell our
thousand records in a disk file, save it and tell our
program to read data from a disk file and not from the
standard input device which is the key board.

Fil C t
File Concepts
 A file structure consists of a number of records with
each record representing a real life entity.
 A record is made up of a sequence of fields or
 A record is made up of a sequence of fields or
attributes (e.g., student id, name, major, gpa).
 Records in a file could be accessed either sequentially
or randomly.
 Sequential access files store records in some order
(usually in primary key order)
(usually in primary key order)
 For a file to be used in a program/algorithm, the
following steps should be taken:

Fil R l t d P I t ti
File Related Program Instructions
1 D l fil i t i bl l i l i bl
 1. Declare a file pointer variable or logical variable
name. That is, declare a pointer variable to point to
variable of type FILE. Format is:
 FILE *filepointer;
 e.g., FILE *stnptr;
 2 OPEN the file: This step associates the file pointer
 2. OPEN the file: This step associates the file pointer
variable with a disk file which is to be opened for either
read ( r), write (w), update (r+) or append (a). Format
for opening a file is:
for opening a file is:
filepointer = fopen (“disk file name”, “mode”);
E.g., stnptr = fopen(“stnrec.dat”, “r”);

3 R d/W it d f /i t th fil
 3. Read/Write records from/into the file:
• Read copies the next record from disk file into the internal
memory variables for processing
Format is: fscanf(filePointer, “format specifiers”, variable list
Format is: fscanf(filePointer, format specifiers , variable list
to be read );
• fprintf(filePointer, “format specifiers”, variable list to be
printed );
• fscanf(stnptr,”%s %s %s %f ”, studentid, name, major,
&gpa);
 4. CLOSE the file
• tells the computer the file is no longer needed. Format is:
fclose(filePointer);
• E.g., fclose(stnptr);

FILE END OF FILE (f f) M k ith fil
 FILE END-OF-FILE (feof) Marker with files
 Data files contain feof marker to indicate there are no more data.
 When testing for feof marker in a file include the file pointer as
parameter E g while (! feof (stnptr))
parameter. E.g., while (! feof (stnptr))
 Loop structures can be used to read lines of records from a file
sequentially as:
sequentially as:
• K=0;
fscanf(fptr,”%s %s”, field1, field2);
while (!feof(fptr)
{
{
K++;
fscanf(fptr,”%s %s”, field1, field2);
}

R d St t
Record Structure
A d h fi ld id ifi d i i bl b
 A record has many fields identified using one variable name but
the fields can be of different data types.
 E.g., record student has fields studentid, name, major (of type
t i ) d ( f t l) d b d l d f ll
string), and gpa (of type real) and can be declared as follows:
• struct student_type {
• char studentid[15];
• char name[20];
• char major[15];
• float gpa;
float gpa;
• } /* of student record type */

R d St t
Record Structure
 To declare a variable of record type, we need to first
define the record structure type as we have done above
for student record type, then secondly, we define a
variable to be of this record type.
variable to be of this record type.
 To define a variable of student record type, we do:
• struct student_type studentvar;
 Now we can assign values to fields of the variable
Student as follows:
f(“% % % %f”
• scanf(“%s %s %s %f”,
studentvar.studentid,studentvar.name,
studentvar.major, &studentvar.gpa);

R d St t
Record Structure
A h lid i b f d h fi ld f h
 Any other valid operations can be performed on these fields of the
record (e.g., print, assignment etc.)
 We can also define an array of student records to store more than
t d t d f ll
one student record as follows:
• struct Record_type record_var[size] ;
• E.g., struct Student-type Student[100];
• To print the record for student number 51, we use:
• printf (“%s %s %s %f”, Student[51].name, Student[51].age,
Student[51.major, &Student[51].GPA]);
[ j , [ ] ]);
 And to read a record variable from a file, we again specify the file pointer
first before listing the fields of the record.
 typedef command can be used to rename a record structure.

Oth D t St t
Other Data Structures
 Data structure specifies the way data are stored in the
computer memory
 Two types of Data Structures are
 Two types of Data Structures are
• 1. Single Valued data types [or Ordinal types]
– have ordinal values with a defined preceding or
g
succeeding value
– E.g. of ordinal types are char, integer, logical
type
type
– Real numbers do not have ordinal values

D t St t
Data Structures
• 2. Structured Data Types
– Strings, arrays and records
each variable has multi values e g an array
– each variable has multi-values e.g., an array
• a. Stacks
• A stack is a list of numbers
A stack is a list of numbers
• All additions and deletions are at one end (top of
stack)

D t St t
Data Structures
• A last-in, first-out procedure
• Operations defined on stack are
Push to add a value to the top of stack and
– Push to add a value to the top of stack, and
– Pop to delete a value from top of stack
• E.g., trace the following procedure on stack data
E.g., trace the following procedure on stack data
structure and show the states of the stack before and
after the procedure.
I h ld b d h b f d i h d
• It should be noted that before data is pushed onto
stack, there has to be room to hold the data
• Also, before data is popped from stack, there is data available
Also, before data is popped from stack, there is data available

D t St t
Data Structures
P h 4
• Push 4
Push 5
Push Y
Pop A
10
A B 2 Y 3
Pop A
push 7
Push 8
push B
push B

b Li k d Li t
b. Linked Lists
 A linked list is a data type where each record points to
its successor except for the last record
 Each record contains a field (the linking field) that
 Each record contains a field (the linking field) that
contains the address of the next record in sequence.
 The link field of the first record points to the second
record, that of the second record points to the 3rd
record, etc. and that of the last record contains zero
meaning it points to no record.
g p
 It is easier to add or delete records from a linked list
file than an array of records

Li k d Li t
Linked Lists
 With the linked list, deleted records are placed in an
empty list and additions are placed in the records that
had been deleted or at the bottom of the file
 Example is Figure 9.1 of course text.

Li k d Li t
Linked Lists
 Record of this type can be declared as follows:
 struct list_type
{char id[15];
{char id[15];
char name[20];
list type *listptr ;
list_type listptr ;
}
 struct list_type *listptr ;

Bi T
c. Binary Trees
 A tree structure uses a top down or hierarchical
structure for data
 Each record is stored as a node of the tree. E.g.
 Each record is stored as a node of the tree. E.g.
g
d k
d k
b
f i l

Bi T
Binary Trees
 A parent node is at a higher level The nodes at a lower
 A parent node is at a higher level. The nodes at a lower
level of a node are its children.
 E.g. g is the root node, d is the parent of b and f. b and f
are children of d.
 A subtree consists of a chain of nodes.
 A b h i th f t t l f
 A branch is a path from root to leaf.
 A binary tree is a tree in which each node has at most
two children
 Each record (a node) contains two link fields, one
pointing to the left node (child) and the other pointing to
th i ht hild
the right child.

Bi T (D l ti
Binary Trees (Declaration
 To declare a variable of type binary tree, we do:
struct btree_type {
char node name[20];
char node_name[20];
btree_type *leftPtr;
btree type *rightPtr;
btree_type rightPtr;
} btree_ptr (pointer to btree_type)
 struct btree_type btree_ptr;

Bi T
Binary Trees


Bi T (C ti Al ith )
Binary Trees (Creation Algorithm)

Bi T (T l Al ith )
Binary Trees (Traversal Algorithms)
 Records stored as binary trees have to be processed
and printed in order
 Processing of these records can be done using tree
 Processing of these records can be done using tree
traversal techniques
 3 tree traversal algrorithms are used
• 1. Preorder (N L R)
• 2. Inorder (L N R)
3 P d (L R N)
• 3. Postorder (L R N)

Bi T (T l Al ith )
Binary Trees (Traversal Algorithms)
 E.g. the order of the binary tree in Fig. 14.13 when
processed in each of these methods are:
 1. Preorder: g d b f k i l
 1. Preorder: g d b f k i l
 2. Inorder: b d f g i k l
 3. Postorder: b f d i l k g
g

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