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MTS 3013
STRUCTURED
PROGRAMMING
INTRODUCTION

Never tire of learning new things. Stretch your
mind. Broaden your experience.

Introduction
 A computer is an electronic device capable of
performing commands given by human.
 Program – Are sequences of instructions and
decisions that the computer carries out to
achieve a task
 Programmer – person responsible in writing a
program

Defining Control Structures
 All computer programs are written using one
or more of three basic structures:
 Sequence
 Repetition
 Selection
 These are called control structures or logic
structures because they control the flow of a
program’s logic.

The sequence structure
 You use it each time you follow a set of
directions, in order, from beginning to end.
 Example – a cookie recipe – you need to
follow each recipe instruction in order,
beginning with the first instruction and ending
the last

 Example – a robot named Didi. Didi can understand
only a specific number of instructions / commands :
walk, turn, sit
 Walk – takes one complete step forward
 Turn – turns 180 degree
 Sit – sits down
 Assume that Didi is facing a chair that is two steps
away from him.
 Write the instructions using only commands that Didi
understands, that direct Didi to sit in the chair.

1. Walk
2. Walk
3. Turn
4. Sit 2 steps
algorithm
A set of step-by-step
instructions that
accomplish a task

The repetition structure
 Example – shampoo bottles typically include
repetition structure in the directions for
washing your hair. Those direction usually tell
you to repeat the “apply shampoo to hair”,
“lather”, and “rinse” steps until your hair is
clean.
 Repetition structure referred to as loop,
directs the computer to repeat one or more
instructions until some condition is met, at
which time the computer should stop
repeating the instructions.

 Example : Didi is facing a chair that is 50
steps away from him. Write the algorithm that
directs Didi to sit in the chair.
 Extra command : repeat x times
 Solution:
 Write “walk” instruction 50 times
 Use the “repeat 50 times.”
1. repeat 50 times:
walk
2. turn
3. sit

The selection structure
 Also called decision structure
 Makes a decision, and then takes appropriate
action based on that decision
 Example: you drive your car and approach an
intersection, whether you need to stop or
proceed.

Example
 Example: Didi is holding either a red or yellow
balloon and that he is facing two boxes. One of the
box is colored yellow and the other is colored red.
The two boxes are located 20 steps away from Didi.
Your task is have Didi to drop the balloon into the
appropriate box. The yellow balloon belongs to the
yellow box and the red balloon belongs to the red
box. After Didi drops the balloon you should return
him to the original position.
 You may add additional instructions to Didi’s
instruction set

The algorithm
1. repeat 20 times:
walk
2. if the balloon is red, do this:
drop the balloon in the red box
otherwise
drop the balloon in the yellow box
3. turn
4. repeat 20 times
walk
5. turn

 Calculate the bonus by multiplying the salary 1%
 Calculate the bonus by multiplying the salary 2%
 If the years employed are greater than or equal to 5,
do this:
 If the years employed are less than 5, do this:
 Otherwise, do this:
 Print the bonus
 Read the salary and years employed
 Repeat for each employee:

Exercise
 Assume a company pays an annual bonus to
its employees. The bonus is based on the
number of years the employee has been with
the company. Employees working at the
company for less than 5 years receive a 1%
bonus, all others receive a 2% bonus. Write
an algorithm that prints each employee’s
bonus. Use only the instructions given:

Problem Solving
 Problem solving involves:
 Analysis
 Algorithm or pseudo code or flow chart or
combination of them.

Problems Analysis
 Identify problems:
 Input
 Output
 Process
INPUT PROCESS OUTPUT

Problem
 Write a program obtain average of 3 numbers
given by a user. Display the 3 numbers and
the average of the numbers.

Problems Analysis
 Input : 3 numbers
 Process : 1. Add 3 numbers
2. Divide sum of the numbers by 3
 Output : Print 3 numbers & average

Algorithm
 Algorithm
 Any computing problem can be done by executing
a series of actions in a specific order.
 A procedure for solving a problem in terms of the
actions to be executed and the order in which
these actions are to be executed is called an
algorithm.
 Is a logical solution that is inline with our daily
language or mother tongue language.

Algorithm
Start
1. Set sum = 0 and average = 0
2. Read 3 numbers: nom1, nom2, nom3
3. Add 3 numbers
4. Calculate the average, average = (sum)/3
5. Print 3 numbers(nom1, nom2, nom3) and
the average
End

Pseudo code
 Pseudo code
 Is an artificial and informal language
 Usually it is use English language
 Quite similar to programming language
 The purpose of pseudo code is to make
humans who do not understand computer
programming can easily understand the flow
of the problem solving.

Pseudo code
START
SET sum = 0, average = 0
INPUT nom1, nom2, nom3
sum = nom1 + nom2 + nom3
average = sum / 3
PRINT nom1, nom2, nom3
PRINT average
END

Flow Chart
 Flow Chart
 It is represents by using geometry shapes with
connected line
 Use a standard symbol

Flow Chart
TERMINAL
Indicates the beginning or end of an algorithm
PROCESS
Indicates an input computational or data
manipulation.
INPUT / OUTPUT
Indicates an input or output operation

Flow Chart
DECISION
Indicates a decision point in the algorithm
CONNECTOR
Indicates an entry to or exit from another
part of the flowchart
FLOW LINES
Used to connect the flowchart symbols and
indicate the logic flow
LOOP
Indicates the initial, final and increment
values of a loop

Example of a flow chart
START
END
sum = 0, average = 0
Input nom1,nom2, nom3
sum = nom1 + nom2 + nom3
average = sum / 3
print nom1,nom2, nom3
print average

Exercise
 Write an algorithm and a flow chart to
calculate and display a volume of a sphere.
Volume = 4/3 x pi x radius x radius , where pi = 3.41

Solution
 Analyze the problem
 Input :
 Process :
 Output :
radius
Calculate volume of a sphere
Volume = 4/3 x pi x radius x radius
print volume of a sphere

Solution (algorithm)
Start
1. Input radius
2. Calculate volume of a sphere
3. print volume of a sphere
End

Solution (Flow Chart)
START
END
pi = 3.41
Input radius
Print volume

Control Structures Flow Chart
 3 types of control structures:
 Sequence structure
 Selection structure
 If
 If… else
 Repetition structure
 For
 While
 Do… while

Flow Chart for Selection
Structure 1
Pseudo code
if condition
statement 1
Condition / Boolean
operator
Statement 1 (inside if
structure)
True
False
Example Pseudo code
if student’s grade is greater than or equal to 60
Print “Passed”

Flow Chart for Selection
Structure 2
Condition / Boolean
operator
true
false
Statement 2 Statement 2
Pseudo code
if condition
statement 1
Else
statement 2
Example Pseudo code
if student’s grade is greater than or equal to 60
Print “Passed”
Else
Print “Failed”

Flow Chart for Repetition
Structure
Condition / Boolean
operator
Statement 1 (inside if
structure)
True
False
Example Pseudo code
While there are more items on the shopping list
Purchase next item and cross it off my list

Module Structure
 Used for a big and complex problem
 Divide the problem into smaller problem –
sub module
 To simplify a problem solving
Module structure Pseudo code
Main module
Call sub module
End of main module
Sub module name
Statements
End of sub module
Main module
Sub module
1
Sub module
2

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