Parameters and Arguments — Procedures and Functions | IGCSE Computer Science

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Past paper frequency (2018 to 2024)

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

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

Both procedures and functions can take parameters.

A parameter is a variable named in the definition of the sub-program; it holds the value passed in by the caller.

An argument is the actual value supplied at the call site.

In CALL CalculateArea(5, 3):

Length and Width are the parameters.
5 and 3 are the arguments.

Parameters can be of any data type

PROCEDURE Greet(Name : STRING, Age : INTEGER)
   OUTPUT "Hello, ", Name, ", you are ", Age, " years old"
ENDPROCEDURE

CALL Greet("Alice", 17)

Multiple parameters in order

The order of arguments must match the order of parameters:

FUNCTION Subtract(X : INTEGER, Y : INTEGER) RETURNS INTEGER
   RETURN X - Y
ENDFUNCTION

OUTPUT Subtract(10, 3)       // 10 - 3 = 7
OUTPUT Subtract(3, 10)       // 3 - 10 = -7 (different result!)

Why parameters matter

Parameters make sub-programs reusable with different inputs. Without parameters, a procedure that calculated the area of a rectangle would only ever work for one specific length and width. With parameters, the same procedure works for any length and any width the caller chooses.