C for Engineers

C for Engineers
Julie Iskander,
MSc. Communication and Electronics

Course Outlines
•
•
•
•
•
•

Introduction to Programming
C Program
Data Types, Variable and Constants
Control Statements and loops and functions
Memory Management and Pointers
Structures

What is a Computer Program?
• Computers are dumb machines.
• A Computer Program is a set of instructions, written in a
language the computer understands, to tell the computer
what to do to solve a problem.
• The approach or method used to solve a problem is called an

algorithm
• Example:
• How to write a program to tell if a number is odd or even?

Programming Language
• Machine Language
• Low-level languages
• High level languages

Compilers
• To support a higher-level language, a special computer
program must be used that translates the statements of the
high-level language program into the particular instructions of
the computer.
• A compiler analyzes a program and then translates it into a
form that is suitable for execution on your particular computer
system.
• Types of errors:
• Syntax error  detected by compiler
• Logical error  is not detected by compiler, but makes code give
unpredicted results.

Programming Methodologies
• Linear Programming
• Structural Programming
• Object Oriented Programming

Software Development Life
Cycle
•
•
•
•
•

Analysis
Design
Implementation
Testing
Maintenance

Dennis Ritchie (1941-2011)
• Designer and original
developer of the C
programming language.
• A central figure in the
development of Unix.
• Was awarded the Turing
Award in 1983, and the
National Medal of Technology
in 1999.
• "Ritchie's influence rivals
Jobs's; it's just less
visible," James Grimmelman
observed on Twitter. "His
pointer has been cast to void
*; his process has terminated
with exit code 0."

C Programming Language
• C is a general-purpose programming language initially
developed by Dennis Ritchie between 1969 and 1973 at AT&T
Bell Labs.
• Its design provides efficient mapping to typical machine
instructions, thus substitutes assembly language,
• Portable, as it is not difficult to write programs that can be
run without change on a variety of hardware
• Most of the Linux and UNIX operating systems are written in
C.

C is a “higher-level language,”
yet it provides capabilities that
enable the user to “get
in close” with the hardware
and deal with the computer on
a much lower level.
“PROGRAMMING IN C”, THIRD EDITION, STEPHEN G. KOCHAN

C Compiler
*.c

compiler

.obj

linker

.exe

Compilers translate an entire file of code all at once, rather than line by
line.
Generate all error messages
Creates an intermediate file, waiting to be linked to any external libraries
needed, to create a final executable file
Linker combines your object file with object files already found in the
libraries.

C Program
PreProcessor

Program Body

#include <stdio.h>

int main()
{
printf(“Hello C ”);
return 0;
}

#include directive
• Tells the compiler to insert another file at this location of your
source code.
• The new inserted code is compiled with the rest of the source
code.
• Also include header files (*.h).
• A header file is a file that contains the function prototype of
the functions defined in the library file before compilation, the
compiler will add the header file contents to the source code.
At compilation, the compiler can check function signatures
against syntax errors.

Program Body
Entry Point of the
program. A program
must contain atleast
on function, main()

int main()
{
variable or constant declaration;
statements;
return 0;
}

All variables
must be
declared before
any statement
is executed

C Comments
• Not executable statement, documents the code
• Ignored by compiler
• Single line Comment
// this is a single line comment

• Multi – line Comment
/* This is a longer comment
That spans across multiple lines
……………………….. */

Data types, Variables ,
Constants

Data types
• There are 5 fundamental data types
1.
2.
3.
4.
5.

char (1 byte)
int (2 bytes)
float (4 bytes)
double (8 bytes)
Void
• Size may differ from platform to another

• Can add type modifier to the data types to alter its meaning
(unsigned, signed, long, short)
• Example
• Signed char  0 to 255
• unsigned char  -127 to 127

Variables
• A place to store data, for further usage.
• Declaring Variables:
• datatype variable_name
• datatype variable_list

• Example:
• int x;
• char a,b,c,e;

• C doesn’t initialize variables.
• After declaring a variable, it can be used multiple times

Variables
Local Variables

Global Variables

• Declared inside a
function
• Available only for the
function.
• Ends with the
function, closing
brackets of the function

• Declared out of any
function
• Available for all functions
• Not recommended to
use it extensively.

Constants
• A fixed value, that can’t be changed at any part of the program
• There are two ways to define a constant value
• As a macro, in the preprocessor using define

• #define PI 3.14
• In a program body

• const int pi=3.14;
• Must be initialized when declared

Statements
• Are executable lines of code
• Ends in ;
• Can be a input statement, expression or operation or output
statement

I/O statements
• Output function: display the results on the screen
• printf()
• printf(“string”,*,data+);
• Example:
printf(“Hello”);
int x=3;
printf(“x is %d”,x);

• Format specifiers
•
•
•
•

%d integer
%f float
%c char
%lf double

• putchar(): puts a character on the screen.
• Example:
• putchar(‘a’) ; or putchar(23);

I/O statements
• Input function: wait for user to enter values and save it.
• scanf(“format-specifier”, address -of-var):
Wait for user to input, must specify the data type of the input
(format specifier) and the address to store value in
• getchar()
Reads one character only from keyboard and wait for carriage
return, character is printed to screen
• getch() (only bc)
Reads one character only from keyboard without waiting for
carriage return, character is not printed to screen
• getche() (only bc)

Reads one character only from keyboard without waiting for
carriage return, character is printed to screen

C Memory Managment
Stack

Heap

Uninitialized data
segment

Global and static
Variables Section
(Initialized Data
Segment)
Executable Code
Section
(Code Segment)

Assignments
• Assignment 1: The history of programming languages.
• Assignment 2: Interpreter Versus Compiler
• Assignment 3: What’s the output of the following:
int a=25, b=3;
printf("%d", a/b*b);
Why?

Lab
• Install Borland C 3.1 or Cygwin
• Write hello.c to print Hello world
• Write a program to print the following with the same format
***********
**Hello all**
***********
with one printf statement. Use escape sequences like n,t,…..etc.
• Fix errors in error1.c and error2.c.
• Write a program to ask user to enter the number of the day in a
year and the program will output the day and month. Assume all
month has 30 days.
• Try writing a function for the previous assignment
• Try casting and operator precedence

if statement
if(condition)
{
statements
}
else
{
statement
}

• Write a program to specify if a number is odd or even
int main()
{
int num;
printf(“Enter a number: ”);
scanf(“%d”, &num);
if(num%2)
{
printf(“Odd”);
}
else
{
printf(“Even”);
}
return 0;
}

Nested if
if(condition)
{
statements
}
else
{
if(condition)
{
statement
}
else
{
statement
}
}

if(condition)
{
statements
}
else if(condition)
{
statement
}
else
{
statement
}

• Write a program to print grade of students according to his
marks
int main()
{
int mark;
printf(“Enter your mark: ”);
scanf(“%d”, &mark);
if(mark>=90)
printf(“A”);
else if(mark>=80)
printf(“B”);
else if(mark>=70)
printf(“C”);
else
printf(“Failed”);
return 0;
}

switch................case
switch(expression)
{
case const1:
{
statement;
break;
}
case const2:
{
statement;
break;
}
case const3:
{
statement;
break;
}
default:
{
statement;
}
}

Write a program to print marks range of
students according to his grade
int main()
{
char mark;
printf(“Enter your mark: ”);
scanf("%c",&mark);
switch (mark)
{
case ‘A’:,
printf(“Marks between 100
and 90”);
break;
}
case ‘B’: ,
and 80”);
break;
}

case ‘C’:
{
and 70”);
break;
}
default:
{
printf(“less than 70”);
}

}
return 0;
}

break
• What if we forget a break in any case?

Fall through
• All sequential cases till the first break or end of cases will be
evaluated

Looping
• Is repeating a block of code for a specific times or until a
condition is satisfied.
• Loops can be terminated using break statement, or an
iteration skipped using continue statement.

for loop
for( initialization ; condition ; increment )
{
statements to be repeated;
}
• Initialization is a statement executed once at the start of the
loop.
• Condition is evaluated before every iteration, to decide to go
on or quit the loop, must evaluate to true/false
• Increment is a statement executed at the end of each iteration
• Used for repeating code a specific number of times

• Write a program to print numbers from 1 to 100
int main()
{
int i;
for(i=1; i<=100 ;i++)
{
printf("%dn",i);
}
return 0;
}

• What’s the output?
int main()
{
int i;
for(i=1; i<=100 ;i++)
{
if(i==10)
continue;
printf("%dn",i);
}
return 0;
}

int main()
{
int i;
for(i=1; i<=100 ;i++)
{
printf("%dn",i);
if(i==10)
break;
}
return 0;
}

int main()
{
int i;
for(i=1; i<=100 ;i++)
{
if(i==10)
break;
printf("%dn",i);
}
return 0;
}

int main()
{
int i=0;
for(; ;)
{
i++;
printf("%dn",i);
}
return 0;
}

• Write a program to take a character and print it till z is
entered?

int main()
{
char c;
for(c=0; c!='z';)
{
printf("Enter a character");
c=getchar();
getchar();
}
return 0;
}

Why do we need to add another getchar()?

• Write a program to calculate the average of marks of 10
students
int main()
{
int i, mark ; int sum=0, avg;
for(i=0; i<10 ;i++)
{
printf("Enter a student mark : ");
scanf(“%d”, &mark);
sum+=mark;
}
avg=sum/10;
printf(“Average of student marks is %d”,avg);
return 0;
}

Nested for loops
What’s the output?
int main (void)
{
int n, number, triangularNumber, counter;
for ( counter = 1; counter <= 5; ++counter ) {
printf ("What triangular number do you want? ");
scanf ("%i", &number);
triangularNumber = 0;
for ( n = 1; n <= number; ++n )
triangularNumber += n;
printf ("Triangular number %i is %inn", number,
triangularNumber);
}
return 0;
}

while loop
while(condition)
{
}
• Used for repeating a block of code until a condition is met, the
condition is tested before executing the block of code.
• The block of code can never be executed

int main()
{
int n,x,i=1,multi=1;
printf(“Enter x:”); scanf(“%d”,&x);
printf(“Enter n:”); scanf(“%d”,&n);
while(i<=n)
{
multi*=x; i++;
}
printf(“y is %d”,multi);
return 0;
}

do…….while loop
do
{
} while(condition);
• Used for repeating a block of code until a condition is met, the
condition is tested after executing the block of code.
• The block of code is executed at least once

What is the error in
this code?

int main()
{
int n,x,i=1,multi=1;
printf(“Enter x:”); scanf(“%d”,&x);
printf(“Enter n:”); scanf(“%d”,&n);
do{
multi*=x; i++;
} while(i<=n);
printf(“y is %d”,multi);
return 0;
}

Functions
• Is a block of code, that does a specific task.
• Each program has atleast one function , main
• Functions reduce duplicate code and make maintenance and
modification easier and quicker
• Any function has:
•
•
•
•

Function name
Return type
List of input arguments
body

Functions
• Function definition

Return_type fun_name(list of args)
{
function body
return statement
}
• A function can be defined before the main.
• If defined after main, add a signature before the main. Used
by compiler to check for syntax errors.
• The return statement terminates the function and returns
control to the calling function, is used to return a value

Write a function to print a message
#include <stdio.h>
void sayhi(void);
int main()
{
int a,b,y;
sayhi();
}

void sayhi(void);
{
printf(‘hi from function’);
}

Write a function to add 2 numbers
#include <stdio.h>
int add(int x, int y);
int main()
{
int a,b,y;
printf(“enter 2
numbers”);
scanf(“%d”, &a);
scanf(“%d”, &b);
y=add(a,b);
printf(“the sum is %d”,y)
}

int add(int x, int y)
{
int z;
z=x+y;
return z;
}
What happens in the
memory during
execution?

Passing values to a function
• Call by value
• Where the whole data type is sent to the function and stored as a
local variable to the function, a copy is made.
• Changes done in the function as no effect on the original
variables of the calling function

• Call by address
• Only the address of the argument is sent and stored with the
function
• Changes in the function affects the original variable in the calling
function as it is referenced by its address
• The calling and called functions access the same memory address

Call by address
• Both references the same memory location.

Calling function
x

Called function
Address
of x

Call by value
• Each has it’s own version of the argument.

Calling function
x

Called function
x

Assignments
• Assignment 1: What is a conditional operator or ? Operator ?
• Assignment 2: What are the pros and cons of using call-byvalue and call-by-address?

Lab
• Fix the errors in error1.c and error2.c
• Write a function to calculate the factorial of n, use this function in
main.
• Write a function to reverse the digits in a given number, use this
function in main.
• Write a function that draws a MagicBox table, given its
dimension, use function gotoxy to e able to draw it on the screen.
• Write a program that inputs 5 numbers then prints out the min
and max.

Magic Box
6

1

8

7

5

3

2

9

4

• The size must be odd eg. 3x3, 5x5, 7x7, …………….
• Number 1 is put in row= 1 and col = (size+1)/2
• Numbers from 2 till size*size are put acc. to the
following rule
• If(number-1)%size ==nonzero
• row-1 and col-1
• Or else
• row+1

Static Variables
and Functions

Scope Rules
• All functions are global , no nested functions in C
• A function’s code is private to the function, can’t be accessed by
other functions
• Variables declared inside a block of code, is local to that block.
They’re destroyed at the end of the block of code.
• The input arguments of a function are local variables to it, declared
in the definition of the function.
void func1()
{
int x;
x=10;
}

void func2()
{
int x;
x=-1999;
}

• The variable x is declared twice, with no relation to each other. Each
one is stored in a separate memory location and func1 can’t access
the x in func2.

Scope Rules
• Global variables are declared out of all functions and can be
accessed by all.

What is the output?
int count;
int main()
{
count=100;
printf("In main, count is
%dn", count);
func1();
printf("After func1 call in
main count is
%dn", count);
}

void func1()
{
printf("In func1, count is %dn",
count);
func2();
printf("In func1 after func2 call,
count is %dn", count);
}
void func2()
{
int count=2;
printf("In func2, count is %dn",
count);
}

Static Variables
• Are permanent variables within their own functions or file.
• Not accessible to functions outside their function.
• Maintain their values between function calls.

What is the output?
int main()
{
printf(“series is %d ", series());
printf(“series is %d", series());
}

int series()
{
int num=0;
num=num+23;
return num;
}

What is the output now?
int main()
{
}

int series()
{
static int num=0;
num=num+23;
return num;
}

Recursive Functions
• A function that calls itself.
• Must contain a condition, to ensure a finite execution.
• Example: factorial function
• 5! = 5*4*3*2*1

• Using for loop
int t=5, ans=1;
for(; t>=1;t--)
{
ans*=t;
}

• 5! = 5*4! = 5*4*3!= ………………………..

Recursive Functions
• Since
• 5! = 5*4! = 5*4*3!= ………………………..
• Then we can use recursive functions
• Where n is multiplied by factorial n-1

• What is the terminating condition ?
• N reaches 1

double power(double x, int n)
{
if(n==0)
return 1.0;
return x*power(x, n-1);
}

Arrays
• A collection of variables of the same type, stored
consecutively in the memory and referenced by a single name
• Single Dimensional Arrays
• Datatype varname[size]

• Size must be a constant , can’t be a variable and can’t be
changed at runtime.
• Example:
• int ar[5]
Allocates 5 integer addresses in the memory.

• Elements are accessed by indexing the array name, index are
zero based
• ar[0]  1st elelment
• ar[3]  4th element

Arrays
• Take care that C doesn’t check for out-of –boundary errors. It
is the programmer’s responsibility.
• For loops are closely related to arrays since it is used to
sequentially read/write array elements.

• Remember:
first element

the name of the array is the address of the

Write a program that fills an array with numbers
from 1 to 100, then print them to the screen.
int main()
{
int x[100];
int t;
for(t=0;t<100;t++)
{
x[t]=t+1;
}
for(t=0;t<100;t++)
{
printf(“%dn”, x*t+);
}
}

Write a program that let user input 5 employee
salaries and calculate sum of salaries.
int main()
{
float sum=0;
float salary[100];
int t;
for(t=0;t<5;t++)
{
printf(“Enter Salary: ”); scanf(“%f”, &salary*t+);
}
for(t=0;t<5;t++)
{
sum+=salary[t];
}
printf(“nSum of Salaries: %f”,sum);
return 0;
}

Array Initialization
• int ar[5]={1,2,3,4,5};
• int ar[]={1,2,3,4,5};
• int ar[5]={1,2,3};
 the rest of the elements are initialized to zero.

2D Array
• datatype varname[size1][size2]
• Example:
int ar[5][10];
 2D array of size 5 rows and 10 cols
• For 2D arrays we need to use nested for loops.
• Accessing a 2D array element through 2 indexes.
• ar[1][2] is elemetn in 2nd row, 3rd column

Write a program to fill a 3x4 array with numbers 112 and print them
int main()
{
int row,col,count=1,num[3][4];
for(row=0;row<3;row++)
{
for (col=0;col<4;col++)
{
num[row][col]=count++;
}
}
{
for (col=0;col<=4;col++)
{
print(“%dt”,num[row][col]);
}
}
return 0;
}

Write a program to fill a 3x4 array with numbers 112 and print them in reverse order
int main()
{
{
{
}
}
for(row=2;row>=0;row--)
{
for (col=3;col>=0;col--)
{
}
}
return 0;
}

Write a program to fill a 3x4 array with numbers 112 and print them in col by col order
int main()
{
{
{
}
}
{
for(row=0row<=3;row++)
{
}
}
return 0;
}

2D Array initialization
• int ar[3][5]={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
• int ar[3][5]= {{1,2,3,4,5},{6,7,8,9,10},{11,12,13,14,15}};

Passing arrays to functions
• We can’t pass the whole array values to a function, we just
pass the address of the first location.
• Examples
• void fun1(int ar[])
• int fun2(char carr[])
WHY?????
• void fun3(int ar[][4])  must give the second dimension.

void fun1(int x[])
{
int t;
for(t=0;t<5;t++)
x[t]=t+1;
}
int main()
{
int x[5]={1,2}; int t;
for(t=0;t<5;t++)
printf("%dn", x[t]);
fun1(x);
for(t=0;t<5;t++)
printf("%dn", x[t]);
return 0;
}

Characters in Memory
• Characters are stored in their ascii codes. Each key on the
keyboard has a representation in ascii codes.
A65, a97, ~126

• C stored characters in one byte.
• C divides keyboard keys into 2 categories
• Normal keys:
• When pressed only one byte is sent to the buffer.
• 0 -> 32 control characters
• 33 -> 127 printable characters

• Extended keys
• When pressed sends two bytes to the buffer, the first one as a
null(‘0’) or 0 ascii code.

What is the output?
int main()
{
char c;
c=getch();
if(!c){
printf("extended key");
c=getch();
printf("%d",c);
}
else printf("normal key %d",c);
return 0;
}

Write a program that prints the
characters from Ascii 60 to 80.
int main()
{
int i;
for(i=60; i<=80;i++)
{
printf(“%c  %dn”, I,I);
}
return 0;
}

Character Library - ctype.h
•
•
•
•
•
•
•
•
•

isalnum
isalph
isdigit
isspace
isprint
islower
isupper
toupper
tolower

Strings
• C doesn’t have a data type called strings
• To define a string , define an array of characters
• Example:
• char a[10]  defines a string of 9 characters and a terminating
null character
• Must always add an element for null
• char str*+=“hello”;
 reserves 5+1=6 bytes to save the array

• char str*+=,‘h’,’e’,’l’,’l’,’o’-;
incorrect initialization since no null character to terminate string,
causes unpredictable o/p

• char str*6+=,‘h’,’e’,’l’,’l’,’o’-;
adds a null automatically

printf and scanf
• To print a string, instead of character by character
• Use “%s” format specifier with printf()
• Use puts()

• To input a string, instead of character by character
• Use “%s” format specifier with scanf()
• Use gets();

• Remember: name of string is a pointer to first char element

string.h
•
•
•
•

strcpy
strcat
strlen
strcmp

Write a program input first and last
name to print the full name
int main()
{
char fname[10], lname[10], full[20];
scanf(“%s”,fname);
scanf(“%s”, lname);
strcpy(full,fname);
strcat(full,” “);
strcat(full,lname);
printf(“%s”,full);
return 0;
}

Assignments
• Assignment 1: Search for Fibonacci Numbers, write a function
to generate an array of them

Lab
• Write a program to calculate volume of 5 rooms, first save
width, breadth and height of each room.
• Write a function for the previous program to take the 2d array
describing the rooms and return the sum of volumes.
• Write a function to create a serial-number generator, where each
call to the function returns a number incremented by 23.
• Write a function to ask user for his name and input it character by
character into an array, then print it in uppercase as a string.

Bonus
• Write a program to print the following menu and navigate
through it using UP,DOWN arrows. ESC ends the program.
Enter prints the users choice. If Enter is pressed on Close, the
program ends too.
Open
Edit
Save
Close

Pointers
• Is a variable carrying the address of another.
• Declaring a pointer, using * unary operator
int count=10;
int * int_pointer;
int_pointer=&count;

Pointers
int count=10;
int * int_pointer;
int_pointer=&count;
int x;
x=*int_pointer ;

• Remember
• * in declaration of variable denotes a pointer declaration
• * pointer_var in any statement denotes the value the pointer
points at
• & count denotes the address of count

int main (void)
{
int count = 10, x;
int *int_pointer;
int_pointer = &count;
x = *int_pointer;
printf ("count = %d, x = %dn", count, x)

}

int main ()
{
char c = 'Q';
char *char_pointer = &c;
printf ("%c %cn", c, *char_pointer);
c = '/';
*char_pointer = '(';
return 0;

}

Pointers and Arrays
int values[10]={1,2,3,4,5,6,7,8,9,10};
int *pv=NULL;
pv=values or
pv=&values[0];

• To assign a pointer to an array we declare a
pointer to the data-type of the array, then
assign it to the first element

int arraySum (int array[], const int n)
{
int sum = 0, *ptr;
int * arrayEnd = array + n;
for ( ptr = array; ptr < arrayEnd; ++ptr )
sum += *ptr;
return sum;
}
int main ()
{
int values[10] = { 3, 7, -9, 3, 6, -1, 7, 9, 1, -5 };
printf ("The sum is %dn", arraySum (values, 10));
return 0;
}

Accessing Elements
• values[3]  *(valuesPtr+3)  to access value stored in 4th
location
• &value[2]  values+2  address of 3rd element.
• We can use either way as they are both equivalent

Operations on Pointers
• Add or subtract integer values from pointers.
• Compare two pointers to see if they are equal or not, or if one
pointer is less than or greater than another pointer.
• subtracting two pointers of the same type, the result is the
number of elements contained between the two pointers.
• Examples:
•
•
•
•

p1=&values[2];
p2=&values[7];
p1+4  &values[6] as an address to this element
p2-p1  5 as an integer

Write a function to count string
length using pointers
int stringLength (char *string)
{
char *cptr = string;
while ( *cptr ) ++cptr;
return cptr - string;
}
int main (void)
{
printf ("%d ", stringLength ("stringLength test"));
printf ("%d", stringLength (""));
return 0;
}

Note
• Arrays are passed to functions as addressed
(Call-by-address) always
int fun1(int ar[]) == int fun1(int * ar)

• For better performance,
• If we deal with arrays sequentially  use
pointers
• If we deal with arrays randomly  use Index.

Pointers and Functions
• Revisiting Call-by-address
• Pointers are passed to a function as arguments.
• The contents of the address can be accessed freely from
within the function.

Write a function to swap 2 numbers.
void swap(int x, int y);
int main()
{
int a=5, b=7;
swap(a,b);
printf(“a= %d and b= %d”,a,b);
return 0;
}
void swap(int x, int y)
{
int temp;
temp=x;
x=y;
y=temp;
}

?

Write a function to swap 2 numbers.
void swap(int *x, int *y);
int main()
{
int a=5, b=7;
swap(&a, b);
printf(“a= %d and b= %d”,a,b);
return 0;
}
void swap(int *x, int *y)
{
int temp;
temp=*x;
*x=*y;
*y=temp;
}

Returning Pointers
• Never return a pointer to a local variable.

void test (int *int_pointer)
{
*int_pointer = 100;
}
int main (void)
{
int i = 50, *p = &i;
printf ("Before the call to test i = %dn", i);
test (p);
printf ("After the call to test i = %dn", i);
return 0;
}

What do this program do?
char* match(char c, char *c);
int main()
{
char s[10], *p, ch;
gets(s); ch=getchar();
p=match(ch,s);
if(*p) printf(“%s”,p);
else printf(“No match
found”);
return 0;
}

char * match(char c , char*s)
{
while(c!=*s && *s)
s++;
return (s);
}

Array of Strings/Pointers

char *days[] =
{
"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday",
"Friday", "Saturday" };

Dynamic Allocation
• A program can obtain memory while running.
• Memory allocated in the heap.
• Gives us the flexibility of allocating a variable amount of
memory in the runtime.
• stdlib.h
• void * malloc(numbytes)
• void free(void* )

Write a program to allocate an
integer.
int main()
{
int *pn=NULL;
pn=(int)malloc(sizeof(int));
if(!pn)
printf(“Out of memory”);
else
{
scanf(“%d”, pn);
printf(“%d”, *pn);
free(pn)
}
}

Note
• It is your responsibility to free any allocated
memory.

To allocate an array
int *pn;
pn=(int *)malloc(10*sizeof(int));

free(pn)

To allocate a variable length array of
names( variable length too)
char **names; int len;
int n =5; //number of names
names = (char **)malloc(n*sizeof(char*));
for(i-0; i<n;i++){
scanf(“%d”,&len);
names[i]= (char *)malloc(len*sizeof(char));
}

Pointer to pointer

Structure
• Is a group of variables under one name and is called an
aggregate data type.
• Structure Declaration:
• Must declare a template to be used to create structure variables.
• The declaration must be global so that all functions can use it.
struct struct_name
{
type var1;
type var2;
type var3;
} ;

Structure
• Example
struct addr
{
char street[10];
int streetNo;
char city[20];
} ;

Declaring a struct variable
• Declaration use keyword struct with name of structure
• struct addr addr1;
• addr1 is a variable, allocated space in the memory according to
data types defined in the struct addr declaraion

• Accessing elements inside structures using “.” dot notation.
• addr1.streetNo=3;
• strcpy(addr1.street,“New street”);
• strcpy(addr1.city,“Alex”);

Write a program to get your address
then print it on the screen
struct addr{
char street[40];
int streetNo;
};
int main()
{
struct addr myaddr;
printf(“Enter your address:n Street: ”);
scanf(“%s”,myaddr.street);
printf(“Street No: ”);
scanf(“%d”,&myaddr.streetNo);
printf(“The address entered is Street %s no. %d ”,
myaddr.street, myaddr.streetNo);
}

Arrays
• Declaring an array of 10 elements of struct addr
• struct addr arr[10];

• To access streetNo of element 3
• arr[2].streetNo=7

Functions
• Passing a structure as an argument to a function can be done by callby-value or call-by-address like a normal variable.
• Example:
void func1(struct addr x)
{
printf(“Address is : %d %s”, x.streetNo, x.street);
}
int main()
{
struct addr add;
add.streetNo=5;
strcpy(add.street,“My street”);
func1(add);
return 0;
}

Pointer to structure
• Declaring a pointer to structure
• struct addr * padd;

• To access elements, we use “->” arrow operator.
• padd->streetNo=6;

• Don’t forget that before using the pointer it must be assigned
an address of a structure, or dynamically allocated. NEVER

use unassigned pointers.

Example
struct date
{
int month;
int day;
int year;
};

int main()
{
struct date today, *datePtr;
datePtr=&today;
datePtr->month =10;
datePtr->day =2;
datePtr->year=2013;
printf(“Today is %d-%d-%d”, datePtr>day,datePtr->month,datePtr->year);
return 0;
}

Structures containing a pointer
struct mys
{
int *p1;
int * p2;
};
int i1=100, i2=200; struct mys s;
s.p1=&i1;
s.p2=&i2;
*s.p2=88;
printf ("i1 = %d, *s.p1 = %dn", i1, *pointers.p1);
printf ("i2 = %d, *s.p2 = %dn", i2, *pointers.p2);

Nested structures and arrays
• A structure can contain another structure (must be declared
before it) or array.
• Example:
struct addr{
char street[10];
int streetNo;
};
struct student{
char name[20];
int marks[5];
struct addr homeaddress;
};

Nested structures and arrays
• To access elements in a variable of type struct employee
struct student st1;
strcpy(st1.name,“Ahmed”);
st1.marks[3]=100;
st1.homeaddress.streetNo=20;

Assignments
• Assignment 1: How can we initialize Structures and Array of
structures?
• Assignment 2: What are pointers to functions
• Assignment 3: Read on linked lists on page 244. Write a
program to traverse a Linked List and Search for a value in it.

Lab
• Write a function trim4 that takes a string and truncates the
characters after the 4th and returns the new truncated string
without changing the original.
• Write a function that reverse a string using pointers.
• Create the following structures:
• date(int day, int month , int year),
• Student(int serial, char[] name, int marks)
• school(student* students, int numofStudents , char[] address, char
name[] )

• Write a function to fill data of a school.
• Write a function to print data of a school.
• Write a program to fill and print data of n schools (Bonus))

Bonus
• Add Highlighting to the previous Menu bonus
• Hint: Search for the following functions can be helpful
textattr(), textcolor(), textbackground()

C for Engineers

More Related Content

What's hot

Viewers also liked

Similar to C for Engineers

More from Julie Iskander

Recently uploaded

C for Engineers

Editor's Notes