Naming variables

Each is named so it is clear which variable is being used at any time. It is important to use meaningful names for variables:

For example, pocketMoney = 20 means that the variable ‘pocketMoney’ is being used to store how much pocket money you have. Right now you have £20.

The name given to each variable is up to the programmer, but ideally a variable name should have meaning, ie it should reflect the value that it is holding.

Variable naming rules

There are some rules about variable names:

Consistency: ‘name’ is not the same as ‘Name’ or ‘NAME’.
Spacing: variable names should not have a space in them. Use underscores or instead, eg total_money; totalMoney).
Digits: variable names should not start with a digit.
Variable names should start with a lowercase letter.

Consider these example variable names, all of which could be variable names to store the length of a side of a square:

Variable name	Comment
l	A poor choice – it has no meaning
length	Okay but a bit vague
side_length	Good
sideLength	Good
side length	Wrong – don’t use spaces

Variable name	l
Comment	A poor choice – it has no meaning

Variable name	length
Comment	Okay but a bit vague

Variable name	side_length
Comment	Good

Variable name	sideLength
Comment	Good

Variable name	side length
Comment	Wrong – don’t use spaces

Example

This (3.x) program uses two meaningful names when calculating the perimeter of a square:

>>> side_length = 5
>>> perimeter = side_length * 4
>>> print(perimeter)
20

Because meaningful names have been used in this code, it is easy to know what each variable is used for.

Data types

Variables come in all shapes and sizes. Some are used to store numbers, some are used to store text and some are used for much more complicated types of .

The to know are:

String (or str or text). Used for a combination of any characters that appear on a keyboard, such as letters, numbers and symbols.
Character (or char). Used for single letters.
Integer (or int). Used for whole numbers.
Float (or Real). Used for numbers that contain decimal points, or for fractions.
Boolean (or bool). Used where data is restricted to True/False or yes/no options.

Different data types can occur in a real-life database example. In a film database, string links to title, float or real links to rating, integer links to times viewed and Boolean links to favourite.

In many variables must be before they can be used, for example:

Visual Basic - dim score as int
Java – int score;

In some languages, such as Python, you can simply start using the variable without declaring it.

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Programming basicsNaming variables