In this guide:
1. What is a Variable?
A variable is simply a named location in the computer's memory where data can be stored, changed, and retrieved while a program is running. Think of it like a labeled box where you can put a value inside.
2. Identifier Naming Rules
In the Cambridge syllabus, the name you give to a variable or constant is called an identifier. You cannot just name a variable whatever you want. Examiners look for these strict rules:
- Must contain only letters, numbers, and underscores (No spaces!).
- Cannot start with a number (e.g.,
1stPlayeris invalid,Player1is valid). - Should use camelCase or PascalCase to make it readable (e.g.,
HighScoreinstead ofhighscore).
3. Declaring Variables
Unlike modern high-level languages (like Python) that let you create variables on the fly, standard Cambridge pseudocode strictly requires you to declare all variables and their specific data types before you can use them.
// Keyword VariableName : DataType
DECLARE PlayerScore : INTEGER
DECLARE PlayerName : STRING
// Assigning values requires the arrow (←)
PlayerScore ← 0
PlayerName ← "Alice"4. Common Data Types
When declaring a variable, you must specify its data type. Here are the core data types you need to know for your exams:
A whole number without a fractional part. (e.g., 10, -5, 0)
A number that contains a decimal point. (e.g., 3.14, -0.5)
A sequence of alphanumeric characters enclosed in speech marks. (e.g., "Hello World")
A logical value that can only be TRUE or FALSE.
5. Constants
Sometimes you need to store a value that should never change while the program is running (like Pi, or a VAT tax rate). For this, we use the CONSTANT keyword instead of DECLARE. Constants are traditionally written in ALL CAPS.
CONSTANT PI ← 3.142
CONSTANT MAX_PLAYERS ← 46. INPUT and OUTPUT
To make your program interactive, you need to display messages to the screen and read data typed by the user.
DECLARE UserAge : INTEGER
OUTPUT "Please enter your age: "
INPUT UserAge
OUTPUT "Next year, you will be: ", UserAge + 1Exam Strategy: Python vs. Pseudocode
Examiners routinely deduct points for "Syntax Soup." If you learned Python first, you must unlearn these habits for the Cambridge written exam:
| Concept | 🐍 Python (Wrong for Exams) | 📘 Cambridge Pseudocode (Correct) |
|---|---|---|
| Assignment | score = 10 | Score ← 10 |
| Output | print("Hello") | OUTPUT "Hello" |
| Input | age = input("Enter age") | OUTPUT "Enter age" INPUT Age |
Interactive Exam Practice
Scenario: Ask the user for the radius of a circle. Calculate the area (Area = Pi * Radius * Radius) and output the result. Use a constant for Pi.
Hover over the black box to reveal the examiner's solution. Click Run Code to test it instantly in our IDE!
CONSTANT PI ← 3.142 DECLARE Radius : REAL DECLARE Area : REAL OUTPUT "Enter the radius:" INPUT Radius Area ← PI * Radius * Radius OUTPUT "The area of the circle is: ", Area