Algorithms-Flowcharts for programming fundamental

■ 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
ALGORITHMS & FLOWCHARTS

■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.
STEPS IN PROBLEM SOLVING

■ To write a correct program, a programmer must write each and every
instruction in the correct sequence
■ Logic (instruction sequence) of a program can be very complex
■ Hence, programs must be planned before they are written to ensure
program instructions are:
■ Appropriate for the problem In the correct sequence
PURPOSE OF PROGRAM PLANNING

■ 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 & ALGORITHM

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”
end

■ Flowchart is a pictorial representation of an algorithm
■ Uses symbols (boxes of different shapes) that have standardized
meanings to denote different types of instructions
■ Actual instructions are written within the boxes
■ Boxes are connected by solid lines having arrow marks to indicate
the exact sequence in which the instructions are to be executed
■ Process of drawing a flowchart for an algorithm is called
flowcharting
FLOWCHART

The Flowchart
A Flowchart
– shows logic of an algorithm
– emphasizes individual steps and their
interconnections
– e.g. control flow from one action to the next

Oval
Parallelogram
Rectangle
Diamond
Hybrid
Name Symbol Use in Flowchart
Denotes the beginning or end of the program
Denotes an input operation
Denotes an output operation
Denotes a decision (or branch) to be made.
The program should continue along one of
two routes. (e.g. IF/THEN/ELSE)
Denotes a process to be carried out
e.g. addition, subtraction, division etc.
Flow line Denotes the direction of logic flow in the program

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<50
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
Flowchart
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
2
0
ax bx c
  
2
4
b ac


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
Flowchart
■ 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)
4
b b a c
   

DECISION STRUCTURES
■ The expression A>B is a logical expression
■ it describes a condition we want to test
■ if A>B is true (if A is greater than B) we take the action on
left
■ print the value of A
■ if A>B is false (if A is not greater than B) we take the action
on right
■ print the value of B

DECISION STRUCTURES
is
A>B
Print B
Print A
Y N

IF–THEN–ELSE STRUCTURE
■ The structure is as follows
If condition then
true alternative
else
false alternative
endif

IF–THEN–ELSE STRUCTURE
■ The algorithm for the flowchart is as follows:
If A>B then
print A
else
print B
endif
is
A>B
Print B
Print A
Y N

Relational Operators
Relational Operators
Operator Description
> Greater than
< Less than
= Equal to
 Greater than or equal to
 Less than or equal to
 Not equal to

Example 5
■ Write an algorithm that reads two values, determines the largest value
and prints the largest value with an identifying message.
ALGORITHM
Step 1: Input VALUE1, VALUE2
Step 2: if (VALUE1 > VALUE2) then
MAX  VALUE1
else
MAX  VALUE2
endif
Step 3: Print “The largest value is”, MAX

Example 5
MAX  VALUE1
Print
“The largest value is”, MAX
STOP
Y N
START
Input
VALUE1,VALUE2
MAX  VALUE2
is
VALUE1>VALUE2

NESTED IFS
■ One of the alternatives within an IF–THEN–ELSE statement
– may involve further IF–THEN–ELSE statement

Example 6
■ Write an algorithm that reads three numbers and prints the
value of the largest number.

Example 6
Step 1: Input N1, N2, N3
Step 2: if (N1>N2) then
if (N1>N3) then
MAX  N1 [N1>N2, N1>N3]
else
MAX  N3 [N3>N1>N2]
endif
else
if (N2>N3) then
MAX  N2 [N2>N1, N2>N3]
else
MAX  N3 [N3>N2>N1]
endif
endif
Step 3: Print “The largest number is”, MAX

Example 6
■ Draw the flowchart of the above Algorithm.

Example 7
■ Write an algorithm and draw a flowchart to
a) read an employee name (NAME), overtime hours worked
(OVERTIME), hours absent (ABSENT) and
b) determine the bonus payment (PAYMENT).

Example 7
Bonus Schedule
OVERTIME – (2/3)*ABSENT Bonus Paid
>40 hours
>30 but  40 hours
 10 hours
$50
$40
$30
$20
$10

Algorithm:
Step 1: Input NAME,OVERTIME,ABSENT
Step 2: if (OVERTIME–(2/3)*ABSENT > 40) then
PAYMENT  50
else if (OVERTIME–(2/3)*ABSENT > 30) then
PAYMENT  40
PAYMENT  30
PAYMENT 20
else
PAYMENT  10
endif
Step 3: Print “Bonus for”, NAME “is $”, PAYMENT

Example 7
■ Draw the flowchart of the above algorithm?

■ A programmer has to go through the following stages to develop a
computer program:
1. Defining and Analyzing Problem
2. Designing the Algorithm
3. Coding or Writing the Program
4. Testing Program
5. Final Documentation
PROGRAM DEVELOPMENT PROCESS

Algorithms-Flowcharts for programming fundamental

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