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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
otherwisedrop the balloon in the yellow box
3. turn4. repeat 20 times
walk5. 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:
Answer??
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 languageQuite similar to programming languageThe 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 ChartDECISION
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 chartSTART
END
sum = 0, average = 0
Input nom1,nom2, nom3
sum = nom1 + nom2 + nom3
average = sum / 3
print nom1,nom2, nom3print 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 sphereVolume = 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
Volume = 4/3 x pi x radius x radius
3. print volume of a sphere
End
Solution (Flow Chart)
START
END
pi = 3.41
Input radius
Volume = 4/3 x pi x radius x 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 1Condition / Boolean
operatorStatement 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
TQ