Integer, real, Boolean, character and string; variables and constants; MOD, DIV, precedence and Boolean logic.
What you will learn
- Choose the right data type for a value
- Use MOD and DIV
- Work out expressions in the right order
- Evaluate AND, OR and NOT
Five data types
Every value in a program has a data type, which decides what can be done with it.
| Type | Holds | Examples |
|---|---|---|
| Integer | whole numbers | 17, -3, 0 |
| Real (float) | numbers with a decimal part | 8.50, 21.4 |
| Boolean | one of two values | True, False |
| Character | one single character | "B", "?" |
| String | text, any length | "LS1 4AP", "07700 900123" |
A phone number is a string: it starts with 0 and nobody adds phone numbers together.
Casting changes a value's type: str(7) gives the text "7", int("42") gives the number 42. Joining two strings with + sticks them together: "4" + "5" is "45", but 4 + 5 is 9.
So int("3") + int("8") is 11, because both are turned into numbers first. AQA writes these casts as STRING_TO_INT, INT_TO_STRING and STRING_TO_REAL; float() in Python turns text into a real.
A variable is a named place in memory (a named location) whose value can change while the program runs. A constant keeps the same value for the whole run, such as const VAT_RATE = 0.2, so it cannot be changed by mistake and is easy to update in one place.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- Five data types
- Arithmetic, MOD and DIV
- Comparisons and Boolean operators
- Try it: MOD and DIV
7 practice questions, marked as you go; about 20 minutes in all.
Key terms
Data type, Casting, Variable, Constant, DIV, MOD, AND, NOT
In this unit: Programming
Data types, operators, selection, loops, arrays, strings, subroutines, robust programs, SQL and files, read and traced step by step.