Subprograms — Functions and Procedures

Watch first

Craig n DaveSubroutines in pseudocode

Reference & Examples

Why use subprograms?

Avoid repeating code — write once, call many times (reusability).
Break complex problems into smaller parts (decomposition).
Easier to test each part separately.
Easier to read and maintain — meaningful names explain what code does.
Teams can work on different subprograms simultaneously.

Procedures vs functions — fill in the table

Term	Description
Procedure
Function
Procedure example
Function example
Edexcel pseudocode syntax

Parameters and arguments — fill in the table

Term	Description
Parameter
Argument
FUNCTION add(a, b)
result = add(3, 7)
Purpose

Variable scope — fill in the table

Term	Description
Local variable
Global variable
Best practice
Why scope matters
Name clash rule

Procedure — no return value

PROCEDURE greet(name)
    PRINT "Hello, " + name + "!"
    PRINT "Welcome to the program."
END PROCEDURE

// Calling the procedure:
CALL greet("Ander")
// Output:
// Hello, Ander!
// Welcome to the program.

Function — with return value

FUNCTION calculateArea(length, width)
    area = length * width
    RETURN area
END FUNCTION

// Calling the function:
roomArea = calculateArea(5, 3)
PRINT roomArea    // Output: 15

// Can use directly in expression:
PRINT "Area = " + STR(calculateArea(4, 7))

Function with local variable

FUNCTION isPrime(n)
    // n is a parameter — local to this function
    IF n < 2 THEN
        RETURN False
    END IF
    FOR i = 2 TO n - 1
        IF n MOD i == 0 THEN
            RETURN False
        END IF
    END FOR
    RETURN True
END FUNCTION

// The variable i is local — does not exist outside isPrime

Exam practice — 5 questions · 12 marks · 1CP2 Paper 1 style

1 markProcedure vs function1CP2 Paper 1

What is the key difference between a function and a procedure?

A Functions are faster than procedures

B A function returns a value; a procedure does not

C Procedures can have parameters but functions cannot

D Functions are called using CALL; procedures are not

4 marksWrite a function1CP2 Paper 1

Write a function called maxValue that takes two parameters, a and b, and returns the larger of the two values. Show how you would call it to find the larger of 15 and 23. (4 marks)

Hint: FUNCTION keyword, parameters in brackets, IF to compare, RETURN each result. Call it and store/print the result.

+40 XP

1 markLocal scope1CP2 Paper 1

A variable called total is declared inside a function. What happens to it when the function finishes?

A It becomes a global variable

B It is destroyed — it no longer exists outside the function

C It keeps its value and can be used anywhere in the program

D It is automatically returned from the function

4 marksIdentify and fix the problem1CP2 Paper 1

Study this pseudocode: FUNCTION double(n) result = n * 2 END FUNCTION total = double(5) PRINT total Explain what is wrong and write the corrected version. (3 marks)

Hint: The function calculates but does not RETURN. Without RETURN, the calling code gets no value back.

+40 XP

1 markParameter definition1CP2 Paper 1

In the definition: FUNCTION power(base, exponent), what are "base" and "exponent"?

A Arguments

B Parameters

C Global variables

D Return values

Quick recall flashcards

Subprograms — Functions and Procedures

Why use subprograms?

Procedures vs functions — fill in the table

Parameters and arguments — fill in the table

Variable scope — fill in the table

Module complete! 🎉