1. Control Structure Senior Lecturer
Siti Nurbaya Ismail
Senior Lecturer
Faculty of Computer & Mathematical Sciences
Universiti Teknologi MARA Kedah (e): (b):

2. Previously…

3. Examine the following problem
Solution
Kedai Kasut I offers discount to celebrate hari raya. 50% discount is offered for L size shoes. 30% discount for M size and 20% for S size.
The formulas to calculate the new price is basically the same. But the discount rate is different for each size of shoe. Here, the shoes size determines the discount rate, the new price will have to be calculated differently for each shoes size. The formulas can be written as:
New-price ← price – 20% x price OR
New-price ← price – 30% x price
New-price ← price – 50% x price
The three different formulas demonstrate that there are three choices to select when calculating the new price and the three choices are determined by the shoes sizes whether it is L, M or S

4. Examine the following problem
Solution
You just received SPM result. You got a good result. You have many options to further your study.
You have many choices depending on your interest and credentials. If you want to be an engineer, you should choose any engineering courses. If you want to be an expertise in computer science, take any computer science courses. If you want to be a chef, it is advisable to choose culinary discipline, and so on.

5. Selection Control Structure
used when we have a choice to do activities based on certain conditions
shows decision‐making capabilities of the computer
is implemented in an algorithm using the If statement or case statement
* If statement
* shows how to implement it in a pseudocode and a flowchart
variations of selection control structure are:
* One way selection
* Two ways selection
* Multiple selections

6. If Statement: One Way Selection
used when there is only one choice
If the condition is true then the task is performed
If the condition is false, then no processing will take place
a situation where a computer has to do comparison at least between two values and makes a decision
if the condition is true then certain action will be taken (statement 1 until statement n will be executed)
if the condition is false, no action will be done
IF condition
statement(s)
EndIF
this style of writing a program is called indentation
the purpose is to make the program easy to read and to ease debugging process.

7. If Statement: One Way Selection
condition
Representation Flowchart of One Way Selection

8. Condition
A condition is a comparison at least between two values or variables.
To make a condition (comparison between two values), the following relational operator can be used.
Relational operator
Meaning
> 
Greater than
< 
Less than ==
Equals to, is ≤
Less or equals ≥
Greater or equals !=
Not equal

9. Condition Examples of conditions :
There are few special words can be used in a condition like even, odd, negative, positive or divisible.
Examples:
num1 < num2
age is greater or equals to 40
grade equals to ‘A’
grade == ‘A’
grade is ‘A’
status is “excellent”
if ( number is odd )
if ( year is divisible by 4 )
If ( number is positive )
Note:
When we use single character data as in above (iii) (iv) and (v), use single quotes (‘ ‘) and use double quotes( “ “ ) for a string (vi). Condition used in above (iii), (iv) and (iv) are the same.

10. Tracing Algorithm Using One Way Selection
Example 1
Start
Display “Enter 2 numbers : “
Read no1, no2
Initialize sum with 0
If ( no1 is divisible by 2 )
add no1 to sum
EndIF
If ( no2 % 2 == 0 )
add no2 to sum
Display “ The total is “ , sum
End
Test the above pseudocode with the following data : i ii
iii

11. Example 1 Expected Output: The total is 20 The total is 0
Start
Display “Enter 2 numbers :“
Read no1, no2
Initialize sum with 0
If ( no1 is divisible by 2 )
add no1 to sum
EndIF
If ( no2 % 2 == 0 )
add no2 to sum
Display “ The total is “,sum
End
Example 1
Input Data:
i ii iii
no1
no2
no1 is divisible by 2
sum=no1+sum
no2 % 2 == 0
sum=no2+sum
sum 20 17
20/2 √
sum=20=0
17 % 2 ≠ 0 41 63
41/2 ×
63 % 2 ≠ 0 18 24
18/2 √
sum=18+0
24 % 2 ==0
sum=18+24 42
Expected Output:
The total is 20
The total is 0
The total is 42

12. Tracing Algorithm Using One Way Selection
Example2
Start
Display “Enter 3 numbers : “
Initialize sum1, sum2, sum3 with zero
Read no1, no2, no3
If (no1 is divisible by 2 )
set sum1 with no1
EndIF
If ( no2 % 2 == 0 )
set sum2 with no2
If ( no3 is even )
set sum3 with no3
sum = sum1 + sum2 + sum3
Display “ The total is “ , sum
End
Test the above pseudocode with the following data : i ii
iii

13. Example 2 Expected Output: The total is 60 Input Data:
i ii iii
no1
no2
no3
no1 is divisible by 2
set sum1 with num1
no2%2==0
set sum2 with num2
no3 is even
set num3 with no3
sum1
sum2
sum3
sum = sum1+sum2+sum3 20 40 17
20/2 √
sum1=20
40%2==0 √
sum2=40
17 = even x
= = 60

14. Two Ways Selection Have two choices to choose from
However, only one choice can be executed at one time
either to execute the first choice and ignore the second choice
or process only the second choice and ignore the first one
If ( condition )
Statement1(s)
Else
Statement2(s)
EndIF

15. Multiple Ways Selection
In solving a problem, sometimes there are situation that has more than two choices.
This problem can be solve using multiple ways selection.
There are two types of multiple ways selection
Simple if statement
Nested if statement
nested if statement is the scenario where there is if statement inside another if statement

16. Multiple Ways Selection
Simple if statement
If (condition)
Statement(s)
ElseIf (condition) .
Else
EndIF
If (condition)
Statement(s)
ElseIf (condition) .
EndIF

17. Multiple Ways Selection
Nested if statement

18. Multiple Ways Selection
Nested if statement
nested if statement is the scenario where there is if statement inside another if statement

19. Multiple Ways Selection
Nested if statement
nested if statement is the scenario where there is if statement inside another if statement

21. Multiple Ways Selection

22. Multiple Ways Selection

24. EXERCISES