Computer Science (9210) | Data types

Welcome to the World of Data Types!

Hello future Computer Scientists! This chapter is super important because it teaches you the fundamental building blocks of all programming: Data Types.
Think of a computer program as a massive kitchen. To bake a cake, you need to know if you are using flour (a dry ingredient) or milk (a liquid ingredient). If you mix them up, the recipe fails!
Similarly, computers need to know exactly what kind of information they are holding—a whole number, text, or a true/false answer—so they can handle it correctly.

Why Data Types Matter (The Basics)

A Data Type defines the kind of data a variable can hold, how much memory it needs, and what operations (like addition or subtraction) can be performed on it.

1. Memory Efficiency

Computers have limited memory (RAM). An integer (a whole number) takes up less space than a real number (a decimal number). By assigning the correct data type, your program runs faster and uses resources efficiently.

2. Valid Operations

You can multiply two numbers together, but it makes no sense to multiply your name by your address. Data types ensure the computer only tries to perform sensible operations.
Example: You can add Integer 5 + 3. You cannot add String "hello" + "world" (you can only join them together, which is called concatenation).

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The Five Essential Data Types

In your OxfordAQA curriculum, you need to know five main data types. Don’t worry if this seems like a lot; we will break them down one by one!

1. Integer (INT)

The Integer data type is used for whole numbers only.
It cannot store any fractions, decimals, or commas.

• What it stores: Positive and negative whole numbers (e.g., 10, -500, 0).
• Memory Tip: Integers use less memory than Real numbers.
• Real-World Example: Counting the number of students in a class, tracking a year (e.g., 2024), or someone's age.

Key Takeaway: If you don't need a decimal point, use an Integer!

2. Real / Float (REAL)

The Real (often called Float in programming languages) data type is used for numbers that include a decimal point (or a fractional component).

• What it stores: Numbers that are not whole (e.g., 3.14, -0.01, 99.99).
• Real-World Example: Money and currency (e.g., \$15.50), measurements (e.g., height of 1.75 meters), or scientific calculations.

Analogy: Think of Real/Float as money. You often need cents (the decimal part) to be accurate!

3. Boolean (BOOL)

The Boolean data type is the simplest but most powerful type. It can only hold one of two possible values: True or False.

• What it stores: The result of a comparison or condition.
• Only Two Values: TRUE or FALSE.
• Real-World Example: A light switch (On = True, Off = False), checking if a user is logged in (LoggedIn = True), or checking if a number is greater than 10 (IsGreater = False).

Did you know? Boolean values are essential for all decision-making in programming (using IF statements). It's named after the mathematician George Boole.

4. Character (CHAR)

A Character data type is used to store a single letter, digit, space, or symbol.

• What it stores: One item, always enclosed in quotation marks (usually single quotes, ' ').
• Examples: 'A', 'b', '7', '?', ' ' (a space).
• Important Note: Even if a Character stores a number like '7', the computer treats it as a symbol, not a number you can use for addition.

5. String (STRING)

The String data type is the most commonly used type for handling text. It is a sequence (a chain or collection) of Characters.

• What it stores: Any combination of letters, numbers, spaces, and symbols (text).
• Format: Always enclosed in quotation marks (usually double quotes, " ").
• Real-World Example: Names ("Jane Smith"), addresses ("12 High Street"), or error messages ("Access Denied").

String vs. Character: What’s the Difference?

A Character holds exactly one thing (e.g., 'C').
A String holds one or more things (e.g., "CS is Great").

String vs. Integer: Crucial Distinction

This is often where students get stuck. Look at these two examples:

1. Integer Number: Age = 15
2. String Text: Student_ID = "0015"

Even though the String variable Student_ID contains the digits "0015", you cannot perform mathematical calculations on it. It is just text! If you tried to add 1 to it, the computer would likely concatenate (join) them, giving you "00151", not the mathematical result of 16.

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Review and Practice

Understanding data types is the first step to writing efficient and error-free code. If you define your data correctly, the computer knows exactly how to manage it!

Memory Aid: Data Type Checklist

When defining a variable, always ask yourself:
1. Does it need a decimal? (REAL)
2. Is it only a whole number? (INT)
3. Is it just a single True/False answer? (BOOL)
4. Is it text (a word, name, or sentence)? (STRING)
5. Is it just a single key or symbol? (CHAR)