Procedures vs Functions: Side by Side — Procedures and Functions | IGCSE Computer Science

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 4% of your exam marks.

stable

Rare

Stable4%

Writing and calling procedures/functions with parameters is tested in Paper 2.

This comparison appears in almost every Cambridge IGCSE exam paper.

Feature	Procedure	Function
Returns a value?	No	Yes
Keyword used to define	`PROCEDURE ... ENDPROCEDURE`	`FUNCTION ... ENDFUNCTION`
Uses `RETURNS` in header?	No	Yes (`RETURNS <data type>`)
Contains `RETURN <value>`?	Usually no	Yes (the value to send back)
How it is called	With `CALL` keyword	Used inside an expression (no `CALL`)
Typical use	Doing something (output, save, update state)	Calculating something and giving the value back
Example pseudocode call	`CALL CalculateArea(5, 3)`	`Result ← CalculateArea(5, 3)`

If the sub-program's job is to DO something, write a procedure and call it with CALL.
If the sub-program's job is to PRODUCE a value, write a function and use it inside an expression.