Selection Structure
Pseudo-Code

In the mid-1960’s, mathematicians proved that any program, no matter how complicated, can be written using only 3 basic control structures.

• Sequence
• Selection
• Iteration also called repetition

Control structures are used to control which instruction will be executed next.

So far we have only used the sequence structure. The sequence control structure is the default or overriding structure.
 
The sequence structure indicates instructions are to be executed one statement at a time in the order they occur from top to bottom unless a different control structure dictates otherwise.
 
The Selection Structure provides flexibility to our programs. We can do different things depending on the situation.

• People who work overtime are paid more for their overtime hours
• Senior citizens are awarded a discount
• Customers who pay their bill early may receive a discount

We use the word IF followed by a condition to represent the Selection Structure in Pseudo-code. Actions we want to perform when the condition is True are listed following the IF. The conditional statements are usually indented for clarity. We indicate the end of the conditional statements with the words EndIf.

If Age > 65 Then
            ‘conditional statement
            Calculate purchaseAmount = PurchaseAmount – (PurchaseAmount * .1)
End If

Calculate Tax = PurchaseAmount * .075 ‘unconditional statement

Another Example

If HoursWorked > 40 Then
            ‘Conditional statement
            Calculate GrossPay = (HoursWorked – 40) * (PayRate * 1.5) + (40 * PayRate)
End IF

IF HoursWorked <= 40 Then
            ‘Conditional statement
            Calculate GrossPay = HoursWorked * PayRate
End IF
 
Calculate StateTax = GrossPay * .03 ‘unconditional statement