Data types, variables and operators
Every value in a program has a data type, which decides what you can do with it. Operators then do the work: arithmetic on numbers, comparisons that give true or false, and Boolean logic that combines conditions.
Part 1 of 3: Learn it
In short
- The main data types are integer, real (float), Boolean, character and string.
- DIV gives the whole-number part of a division; MOD gives the remainder.
- Casting converts a value from one type to another, such as a string "42" to the integer 42.
Where this is in your specification
Spec points: AQA 3.2.1 to 3.2.5, OCR 2.2.1 and 2.2.2, Edexcel Topic 6
| Board | Topic: Programming in exam style |
|---|---|
| AQA 8525 | 3.2.1 to 3.2.11, 3.7.1 |
| Edexcel 1CP2 | Topic 6 (and Topic 1 for trace tables) |
| OCR J277 | 2.2.1 to 2.2.3, 2.3.1, 2.3.2 |
| Eduqas C500 | 7 Principles of programming; 10 Program construction |
| Cambridge IGCSE 0478 | 8 Programming |
| National 5 C816 75 | Software design and development: implementation, testing |
Data types
| Type | Holds | Example |
|---|---|---|
| Integer | whole numbers | 17, −3 |
| Real (float) | numbers with a decimal part | 3.75 |
| Boolean | one of two values | True, False |
| Character | a single letter, digit or symbol | 'G' |
| String | a sequence of characters | "Year 11" |
Variables and constants
A variable is a named store whose value can change while the program runs. A constant is given a value once and cannot be changed later, such as VAT_RATE = 0.2. Constants make code easier to read and update in one place. Assignment uses = (or ← in AQA pseudocode) to put a value in a variable.
Operators
| Kind | Operators | Example |
|---|---|---|
| Arithmetic | + − * / | 7 / 2 gives 3.5 |
| Integer division | DIV | 17 DIV 5 gives 3 |
| Remainder | MOD | 17 MOD 5 gives 2 |
| Power | ^ | 2 ^ 5 gives 32 |
| Comparison | == != < > <= >= | 4 != 5 gives True |
| Boolean | AND OR NOT | True AND False gives False |
MOD is handy for testing whether a number is even: n MOD 2 is 0 for every even number.
Casting
Input from the keyboard usually arrives as a string. To do arithmetic with it, convert it: int("42") + 1 gives 43, while "42" + "1" joins the strings to make "421". str(), int(), float() and bool() are the usual casting functions.
What is 29 MOD 4?
Show the answer
1 (29 = 7 × 4 + 1).
Part 2 of 3: See it worked
Worked examples
Example 1
A school has 230 students to put on minibuses of 16. Use DIV and MOD to find how many full buses there are and how many students are left over.
- 230 DIV 16 = 14 (14 × 16 = 224)
- 230 MOD 16 = 6
Answer: 14 full minibuses, with 6 students left over (so 15 buses are needed).
Example 2
x = 6 and y = 10. Evaluate (x > 5) AND NOT (y == 10).
- x > 5 is True
- y == 10 is True, so NOT (y == 10) is False
- True AND False
Answer: False.
Common mistakes
- Mixing up DIV and MOD.
- Storing a phone number or a postcode as an integer.
- Using = to compare in languages that need ==.
- Forgetting to cast input before doing arithmetic with it.
Which data type would you use for whether a user is logged in?
Show the answer
Boolean.
Part 3 of 3: Test yourself
Check yourself
Answer each one in your head or on paper first, then open it to check.
What is 29 MOD 4?
1 (29 = 7 × 4 + 1).
Which data type would you use for whether a user is logged in?
Boolean.
What is the difference between a variable and a constant?
A variable's value can change while the program runs; a constant's value is fixed.
Jobs that use this
Each link opens the job profile on the National Careers Service (England). In the rest of the UK: My World of Work (Scotland), Careers Wales, nidirect careers (Northern Ireland).
Diese Lernzettel sind auf Englisch, weil sie britischen Prüfungslehrplänen folgen.
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