Swift Introduction | Values, Variables, and Operations | Variables, Constants, and Types
Declare a variable before using it. Using an undeclared variable or redeclaring an existing variable causes an error.
var variable = value
var variable:Type = value
Variables are usually declared with an initial value. To declare a variable without assigning a value immediately, specify its type.
var variable:Type
Constants
Use a constant when a value must not change later.
let constant = value
let constant:Type = value
Declare a constant and assign its value together. The assigned value cannot be changed afterward.
Variable Types
When declaring a variable or constant, you can specify its type as well as its name. Every Swift variable has a type. If you omit the type in a declaration such as var variable = value, Swift infers it from the assigned value. A declaration containing only var variable is invalid.
Swift is a statically typed language. Each variable has a type and can store only values of that type.
Main Types
Integers
| Type | Description |
|---|---|
| Int | A general integer. Its width is 32 or 64 bits depending on the CPU. |
| UInt | Similar to Int, but unsigned. It cannot represent negative values. |
| Byte | An 8-bit value. |
| Int8, Int16, Int32, Int64 | Integer types with an explicit width. Unsigned types such as UInt8 are also available. |
Floating-Point Numbers
| Type | Description |
|---|---|
| Float | A 32-bit floating-point value. |
| Double | A 64-bit floating-point value. |
| Float32, Float64, Float80, Float96 | Floating-point types used when specifying a width explicitly. |
Text
| Type | Description |
|---|---|
| String | General text. |
| Character | A single character. |
Boolean Values
| Type | Description |
|---|---|
| Bool | A logical value: true or false. |
These can be considered basic types. Swift also supports more complex values such as arrays, objects, tuples, and optionals, which are explained separately.