Selection (if, elif, else, switch/case)

Selection allows a program to make decisions and follow different paths based on conditions. This is one of the three fundamental programming constructs (alongside sequence and iteration) and is required for AQA 3.2 / OCR J277 2.2.

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Why Do We Need Selection?

Without selection, programs can only execute instructions in a fixed order (sequence). Selection lets programs respond to different inputs and situations, making them useful in the real world. For example, a login system must check whether a password is correct before granting access.

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IF Statements

The simplest form of selection is the IF statement, which executes a block of code only if a condition is True.

Pseudocode

IF age >= 18 THEN
    OUTPUT "You can vote."
ENDIF

Python

if age >= 18:
    print("You can vote.")

Key Point: In Python, the colon : at the end of the if line and the indentation of the body are essential. In pseudocode, the block ends with ENDIF.

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IF...ELSE

An IF...ELSE provides two paths — one for when the condition is True and one for when it is False.

Pseudocode