Constants and Variables: Declaring Constants and Variables

Let maximumNumberOfLoginAttempts = 10
var currentLoginAttempt = 0

Must be declared before they’re used.
You can’t declare it again with the same name, or change it to store values of a different type.

Let π = 3.14159
let 你好 = "你好世界"

Var friendlyWelcome = "Hello!"
friendlyWelcome = "Bonjour!"
// friendlyWelcome is now "Bonjour!"

Can contain almost any character, including Unicode characters.
Can’t contain whitespace characters, mathematical symbols, arrows, private-use Unicode scalar values, or line- and box-drawing characters.
They can't begin with a number, although numbers may be included elsewhere within the name.
Avoid using keywords as names unless you have absolutely no choice.
Let languageName = "Swift" languageName = "Swift++" // This is a compile-time error: languageName cannot be changed.

Related concepts

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Declaring Constants and Variables

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