Lecture-8_ Flowchart Algorithm Pseudocode.pptx

ALGORITHMS AND FLOWCHARTS
■A typical programming task can be divided into
two phases:
■Problem solving phase
◻produce an ordered sequence of steps that describe
solution of problem
◻this sequence of steps is called an algorithm
■Implementation phase
◻implement the program in some programming
language

Steps in Problem Solving
■First produce a general algorithm (one can use
pseudocode)
■Refine the algorithm successively to get step by
step detailed algorithm that is very close to a
computer language.
■Pseudocode is an artificial and informal
language that helps programmers develop
algorithms. Pseudocode is very similar to
everyday English.

Pseudocode & Algorithm
■Example 1: Write an algorithm to
determine a student’s final grade and
indicate whether it is passing or failing.
The final grade is calculated as the
average of four marks.

Pseudocode:
■Input a set of 4 marks
■Calculate their average by summing and dividing
by 4
■if average is below 50
Print “FAIL”
else
Print “PASS”

■Detailed Algorithm
■ Step 1: Input M1,M2,M3,M4
Step 2: GRADE ← (M1+M2+M3+M4)/4
Step 3: if (GRADE < 50) then
Print “FAIL”
else
Print “PASS”
endif

The Flowchart
■ (Dictionary) A schematic representation of a sequence of
operations, as in a manufacturing process or computer
program.
■ (Technical) A graphical representation of the sequence of
operations in an information system or program.
Information system flowcharts show how data flows from
source documents through the computer to final
distribution to users. Program flowcharts show the
sequence of instructions in a single program or
subroutine. Different symbols are used to draw each
type of flowchart.

The Flowchart
■ An organized combination of shapes, lines and text which
graphically illustrate a process/program.
■ A type of diagram that represents an algorithm, workflow or process,
showing the steps as boxes of various kinds, and their order by
connecting them with arrows. This diagrammatic representation
illustrates a solution to a given problem.
■ Emphasizes individual steps and their interconnections
■ Flowcharts are used in analyzing, designing, documenting or
managing a process or program. Like other types of diagrams, they
help visualize what is going on and thereby help the people to
understand a process, and perhaps also find flaws, bottlenecks, and
other less-obvious features within it.
■ Very helpful in explaining program to others.

Flowchart Symbols
Different symbols are used for different states in flowchart, For example: Input/Output and decision
making has different symbols. The table below describes most of the symbols that are used in making
flowchart

Example
PRINT
“PASS”
Step 1: Input M1,M2,M3,M4
Step 2: GRADE ← (M1+M2+M3+M4)/4
Step 3: if (GRADE <50) then
Print “FAIL”
else
Print “PASS”
endif
START
Input
M1,M2,M3,M4
GRADE←(M1+M2+M3+M4)/4
IS
GRADE<5
0
PRINT
“FAIL”
STOP
Y
N

Example 2
■Write an algorithm and draw a flowchart to
convert the length in feet to centimeter.
■Pseudocode:
◻ Input the length in feet (Lft)
◻Calculate the length in cm (Lcm) by
multiplying LFT with 30
◻Print length in cm (LCM)

Example 2
■Algorithm
Step 1: Input Lft
Step 2: Lcm ← Lft x 30
Step 3: Print Lcm
START
Input
Lft
Lcm ← Lft x 30
Print
Lcm
STOP
Flowchart

Example 3
■Write an algorithm and draw a flowchart that will
read the two sides of a rectangle and calculate
its area.
■Pseudocode
◻Input the width (W) and Length (L) of a rectangle
◻Calculate the area (A) by multiplying L with W
◻Print A

Example 3
Algorithm
Step 1: Input W,L
Step 2: A ← L x W
Step 3: Print A
START
Input
W, L
A ← L x W
Print
A
STOP

Example 4
■Write an algorithm and draw a flowchart that
will calculate the roots of a quadratic equation
■ Hint: d = sqrt ( ), and the roots are:
x1 = (–b + d)/2a and x2 = (–b – d)/2a

Example 4
Pseudocode:
◻Input the coefficients (a, b, c) of the quadratic
equation
◻Calculate d
◻Calculate x1
◻Calculate x2
◻Print x1 and x2

Example 4
■Algorithm:
Step 1: Input a, b, c
Step 2: d ← sqrt ( )
Step 3: x1 ← (–b + d) / (2 x a)
Step 4: x2 ← (–b – d) / (2 x a)
Step 5: Print x1, x2
START
Input
a, b, c
d ← sqrt(b x b – 4 x a x c)
Print
x1 ,x2
STOP
x1 ←(–b + d) / (2 x a)
X2 ← (–b – d) / (2 x a)

Example 5
■ Draw a flowchart to add two numbers entered by user.
Start
Read a, b
End
sum ← a + b
Declare a, b , sum
Print sum

■ Draw a flowchart to print the
average of three numbers entered
by user.
Start
Read n1, n2,n3
End
sum ← n1 + n2 + n3
avg ← sum / 3
Declare n1, n2 ,n3, sum, avg
Example 6
Print avg

Example 7
▪Draw a flowchart to find the
largest among three different
numbers entered by user.

Start
Read m
End
Declare m, counter=0
Print “n”
is
counter < m
Example 8: Draw a flowchart to print a letter ‘n’ m
times.
counter=counter+1
F
T

Algorithm and Pseudo Code
Example - 9
Problem 1: Given a list of positive numbers, return the largest number on the list.
Inputs: A list L of positive numbers. This list must contain at least one number.
(Asking for the largest number in a list of no numbers is not a meaningful
question.)
Outputs: A number n, which will be the largest number of the list.
Algorithm:
1. Set max to 0.
2. For each number x in the list L,
compare
it to max.
3. If x is larger, set max to x.
4. max is now set to the largest number
in
the list.
Program Segment
def find_max (L):
max = 0
for x in L:
if x > max:
max = x
return max

Example - 10
Add two numbers entered by the user
Step 1: Start
Step 2: Declare variables num1, num2 and sum.
Step 3: Read values num1 and num2.
Step 4: Add num1 and num2 and assign the result to sum.
sum←num1+num2
Step 5: Display sum
Step 6: Stop

Example - 11
Find the largest number among three numbers
Step 1: Start
Step 2: Declare variables a, b and c.
Step 3: Read variables a, b and c.
Step 4: If a > b If a > c
Display a is the largest number.
Else
Display c is the largest number.
Else
If b > c
Display b is the largest number.
Else
Display c is the greatest number.
Step 5: Stop

Example - 12
Step 1: Start
Else
Else
If b > c
Else
Step 5: Stop

Example - 13
Step 1: Start
Else
Else
If b > c
Else
Step 5: Stop

Example - 14
Step 1: Start
Else
Else
If b > c
Else
Step 5: Stop

Example - 15
Step 1: Start
Else
Else
If b > c
Else
Step 5: Stop

Lecture-8_ Flowchart Algorithm Pseudocode.pptx

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