Algorithm Development: Pseudocode, Flowchart, and Examples, Assignments of Computer Science

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ALGORITHMS AND

FLOWCHARTS

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

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 & 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”

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

A Flowchart

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

Example

“PASS”^ PRINT

Step 1: Input M1,M2,M3,M Step 2: GRADE  (M1+M2+M3+M4)/ Step 3: if (GRADE <50) then Print “FAIL” else Print “PASS” endif

START

M1,M2,M3,M4^ Input

GRADE  (M1+M2+M3+M4)/

GRADE<5^ IS 0 “FAIL”^ PRINT

STOP

N^ Y

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 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

Pseudocode :

 Input the coefficients (a, b, c) of the

quadratic equation

 Calculate d

 Calculate x

 Calculate x

 Print x1 and x

Example 4

 Algorithm :  Step 1: Input a, b, c  Step 2: d  sqrt ( )  Step 3: x1  (– b + d) / (2 xa)  Step 4: x2  (– b – d) / (2 x a)  Step 5: Print x1,x

START

a, b, c^ Input

d  sqrt(b x b – 4 xa xc)

Print x 1 ,x 2

STOP

x 1  (– b +d) / (2 xa) X 2  (– b – d) / (2 xa)

b  b  4  a  c

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