Subroutines: Functions and Procedures

What a subroutine is

A named block of code you can call whenever needed.

• Procedure – does a task, returns nothing.
• Function – does a task and returns a value.

Example

FUNCTION area(width, height)
    RETURN width * height
ENDFUNCTION

OUTPUT area(4, 5)      # 20

PROCEDURE greet(name)
    OUTPUT "Hello " + name
ENDPROCEDURE

greet("Sam")           # Hello Sam

Parameters vs arguments

• Parameters – the variables in the definition (width, height).
• Arguments – the actual values passed in (4, 5).

Why use them?

• Reusability – write once, call many times.
• Readability / maintainability – named, self-contained blocks.
• Easier testing – test each part separately.

Local vs global variables

• Local – exists only inside the subroutine (preferred — avoids accidental changes).
• Global – accessible everywhere.

Exam tip

A function returns a value; a procedure does not. Stating this earns easy marks. Reuse and maintainability are the key benefits.