Algorithm and flowchart

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Subject : C.P.U
Topic: Algorithms and Flowchart

Program design
 Program Design Process has 2 phases:
 Problem Solving Phase
 Creates an algorithm that solves the
problem
 Implementation (Coding) Phase
 Translates the algorithm into a
programming language
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Algorithm
Problem Program

Algorithms
 An algorithm is a finite set of steps defining the
solution of a particular problem.
 Need not to belong one particular language
 Sequence of English statements can also be
algorithm
 It is not a computer program
 An algorithm can be expressed in English like
language called pseudo code, in a programming
language or in the form of flowchart.
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Algorithm Vs Program
 What is the difference between an algorithm and a program?
 a program is an implementation of an algorithm to be run on a
specific computer and operating system.
 an algorithm is more abstract – it does not deal with machine
specific details – think of it as a method to solve a problem.
• What is good algorithm?
Efficient algorithms are good, we generally measure efficiency of an
algorithm on the basis of:
1. Time: algorithm should take minimum time to execute.
2. Space: algorithm should use less memory.
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Algorithm Specification
Every algorithm must satisfy the following criteria:
 Input. Zero or more quantities are externally supplied.
 Output. At least one quantity is produced.
 Definiteness. Each instruction must be clear and
unambiguous(Unique meaning).
 Finiteness. An algorithm terminates in a finite
number of steps.
 Effectiveness. Every instruction must be basic enough
to be carried out than, means not so complex.
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Informal definition of an algorithm

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Finding the largest integer
among five integers

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Defining actions in Find Largest algorithm

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Example 1
Write an algorithm that finds the
average of two numbers
Solution:
Average Of Two
Input: Two numbers
1. Add the two numbers
2. Divide the result by 2
3. Return the result by step 2 2
End

Group 13
Example 2
Write an algorithm to change a numeric
grade to a pass/fail grade.
Solution:
Pass/Fail Grade
Input: One number
1. if (the number is greater than or equal to 40)
then
1.1 Set the grade to “pass”
else
1.2 Set the grade to “fail”
End if
2. Return the grade
End

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Example 3
Write an algorithm for grading System
by following method.
Marks range Grade
>=80 A
>=70 & <80 B
>=60 & <70 C
>=50 & <60 D
<50 F

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Algorithm For Grade
Input: One number
1. if (the number is between 80 and 100, inclusive)
then
1.1 Set the grade to “A”
End if
then
2.1 Set the grade to “B”
End if
Algorithm for Grading
Continues on the next slide
Solution

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then
3.1 Set the grade to “C”
End if
then
4.1 Set the grade to “D”
End if
5. If (the number is less than 50)
then
5.1 Set the grade to “F”
End if
6. Return the grade
End

Advantages Of Algorithm
 It provides the core solution to a given problem. This
solution can be implemented on a computer system
using any programming language of user’s choice.
 It facilitates program development by acting as a
design document or a blueprint of a given problem
solution.
 It ensures easy comprehension of a problem solution
as compared to an equivalent computer program.
 It eases identification and removal of logical errors in
a program.
 It facilitates algorithm analysis to find out the most
efficient solution to a given problem.
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Disadvantages Of
Algorithm
 In large algorithms, the flow of program control becomes difficult
to track.
 Algorithms lack visual representation of programming constructs
like flowcharts; thus, understanding the logic becomes relatively
difficult.
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Flowchart
A graphical representation of an algorithm, often
used in the design phase of programming to work
out the logical flow of a program.
 Visual way to represent the information flow
 Make our logic more clear
 Help during writing of program
 Make testing and debugging easy
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Flowchart or program
constructs
 Sequence: The order of execution, this typically refers to
the order in which the code will execute. Normally code
executes line by line, so line 1 then 2 then 3 and so on.
 Selection: Selection, like branching, is a method of
controlling the execution sequence, you can create large
control blocks, using if statements testing a condition, or
switch statements evaluating a variable etc to control and
change the execution of the program depending on this
environment and changing variables.
 Iteration (Repetition): Iteration is typically used to refer to
collections and arrays of variables and data. Repeating set
of instruction. Counting from 1 to 10, you are iterating
over the first 10 numbers. for, while, do-while loops will be
implemented for iteration.
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Flowchart Constructs
(cont..)
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Flowchart Constructs
(cont..)

Example-1
Write an algorithm and draw a flowchart
that will read the two sides of a
rectangle and calculate its area.
Algorithm
 Step 1: Start
 Step 2: Take Width and Length as input
 Step 3: Calculate Area by Width* Length
 Step 4: Print Area.
 Step 5: End
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Example-1
 Step 1: Start
 Step 2: Input W,L
 Step 3: A  L x W
 Step 4: Print A
 Step 5: End
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START
Input
W, L
A L x W
STOP
Print
A

Example-2
 Write an Pseudo code and draw a
flowchart that will take marks of four
subjects and calculate the average.
Then if average marks are greater than
50 then print PASS otherwise print FAIL.
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Example-2
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Step 1: Start
Step 2: Input M1,M2,M3,M4
Step 3: AVG 
(M1+M2+M3+M4)/4
Step 4: if (AVG <50) then
Print “FAIL”
else
Print “PASS”
endif
Step 5: End
START
Input
M1,M2,M3,M4
AVG(M1+M2+M3+M4)/4
IS
AVG<50
STOP
YN
Print
“PASS”
Print
“FAIL”

Example-3
 Write an algorithm and draw a
flowchart to convert the length in
feet to centimeter.
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Example-3
Algorithm
 Step 1: Start
 Step 2: Input Lft
 Step 3: Lcm  Lft x 30
 Step 4: Print Lcm
 Step 5: End
30
START
Input
Lft
Lcm Lft x 30
Print
Lcm
STOP
Flowchart

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
2
0ax bx c  
2
4b ac
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Example-4
Algorithm:
 Step 1: Start
 Step 2: Input a, b, c
 Step 3: d  sqrt ( )
 Step 4: x1  (–b + d) / (2 x a)
 Step 5: x2  (–b – d) / (2 x a)
 Step 6: Print x1, x2
 Step 7: End
4b b a c   
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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)

Flow Chart`s Limitation
 For very large program, flow chart goes
for many pages
 Costly to draw flow charts for large
program
 Difficult to modify
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Algorithm and flowchart

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