Data Types and Operations

2a - Programming Basics

Variables and Data Types

All data a program uses must be stored in memory.

Each location is given a unique identifier whilst the program is running.

If the value of the data stored at this location may change as the program is running, these are called variables.

Each variable has a data type, that defines what operations can be done on the data.

For example, you can multiply two numbers together but you cannot multiply two words together. The data type tells the computer this.

Some programming languages require variables to be declared at the start of the program.

This allows the computer to allocate the necessary memory as the program starts.

Example:

dim num1 as integer
dim length as float
dim choice as char
dim username as string
dim found as boolean

Some programming languages (e.g. Python) do not need the variables declared, they work it out from the data.

A whole number

e.g. 3, 45, -435

Typically 2 or 4 bytes of memory used (16 or 32 bits)

A number with a fractional part.

e.g. 34.654, -9.5, 3.100

Typically 4 or 8 bytes of memory used (32 or 64 bits)

A single character, where a character can be any letter, digit, punctuation mark or symbol that can be typed

e.g. '4', 'a', '?', '÷'

Typically 1 byte of memory used (8 bits)

Zero or more characters, can be null (empty), one or more characters

e.g. '', 'a', 'the sun is shining!', ' '

Typically 1 byte of memory used per character

A Boolean variable has the value 'True' or 'False'

Typically 1 byte of memory used

This table shows some of the data types and the typical amount of memory each needs.

Data type	Type of data	Typical amount of memory
integer	A whole number, such as 3, 45, -435	2 or 4 bytes
real/float	A number with a fractional part such as 34.456, -9.2, 4.10	4 or 8 bytes
char/ character	A single character, where a character can be any letter, digit, punctuation mark or symbol that can be typed	1 byte
string	Zero of more characters. A string can be null (empty)	1 byte per character
Boolean	A Boolean variable has the value True or False	1 byte

In most programming languages, values are assigned to variables using an '=' sign.

x = 1
pi = 3.142
alpha = 'a'
street = 'Elm Street'
over18 = True

Note: x = 1 means assign the value of 1 to the variable x.

In pseudocode, we use the symbol ← to mean assignment, for example:

x ← 1