Subroutines:
Functions & Procedures

Parameters · Return Values · Local/Global Scope · Benefits of Subroutines

CSZoneEdexcel GCSE Computer Science 1CP2

Functions vs Procedures

Two Types of Subroutine

Function: a named block of code that performs a task and returns a value. e.g. calculate area and return the result.

Procedure: a named block of code that performs a task but does not return a value. e.g. print a welcome message.

def calculate_area(length, width): # function
return length * width

def print_greeting(name): # procedure
print("Hello,", name)

Parameters & Arguments

Passing Data into Subroutines

def add(a, b): # a, b are PARAMETERS
return a + b

result = add(3, 5) # 3, 5 are ARGUMENTS
print(result) # 8

Parameter: variable in the function definition (placeholder)

Argument: actual value passed when calling the function

Functions can take multiple parameters, separated by commas

Local & Global Variables

Scope in Subroutines

Local variable: declared inside a subroutine — only accessible within that subroutine. Created when called, destroyed when it returns.

Global variable: declared outside subroutines — accessible from anywhere. Use sparingly; makes debugging harder.

Edexcel favours using parameters rather than global variables — better practice, more modular code

Exam Practice

Have a go at this question

Edexcel-style question

State two benefits of using subroutines in a program.

2 marks

Any two from: Avoids code repetition — write once, call many times [1]. Makes programs easier to read, understand, and maintain [1]. Allows different programmers to work on different subroutines simultaneously [1]. Easier to test individual sections [1].

Key Takeaways

What to Remember

Function: returns a value; Procedure: no return value

Parameters = placeholders in definition; Arguments = values passed when calling

Local scope: inside only; Global scope: accessible everywhere

Benefits: reduces repetition, improves readability, easier testing