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Variables
A variable associates a name with a value of a particular type. There are two main ways to create variables in Swift. let and var. To declare constants use the let keyword. To declare mutable variables use the var keyword.
The benefit of having two ways to store variables in Swift is to prevent errors of changing variables that should be constant.
let daysInAWeek = 7
var amountOfMoney = 100
amountOfMoney = 150
// amountOfMoney is now 150
daysInAWeek = 10
// This gives us an error!
In this case the variable daysInAWeek should be a constant because there are only seven days in a week, while the variable amountOfMoney should be a var because the amount of money in one's account changes.
Constant and variable names can contain almost any character, including Unicode characters:
let π = 3.14159
let 你好 = "你好世界"
let 🐶🐮 = "dogcow"
To test if your variables have the correct value, use print().
let money = 50
print(money)
// This prints 50
Swift 4 supports the following basic types of variables:
Int or UInt − This is used for whole numbers. More specifically, you can use Int32, Int64 to define 32 or 64 bit signed integer, whereas UInt32 or UInt64 to define 32 or 64 bit unsigned integer variables. For example, 42 and -23.
Float − This is used to represent a 32-bit floating-point number. It is used to hold numbers with smaller decimal points. For example, 3.14159, 0.1, and -273.158.
Double − This is used to represent a 64-bit floating-point number and used when floating-point values must be very large. For example 3.14159, 0.1, and -273.158.
Bool − This represents a Boolean value which is either true or false.
String − This is an ordered collection of characters. For example, "Hello, World!"
Character − This is a single-character string literal. For example, "C"