The best Swift constant Tutorial In 2024, In this tutorial you can learn Constant declaration,Type annotation,Named Constant,Constant output,

Swift constant

Constant Once set, the program is running you can not change its value.

Constants can be of any type of data, such as: integer constant, floating-point constants, character constants or string constants. There are also enumerated type constants:

Constants are like variables except that the value of a constant can not be changed once set, and the value of a variable can be altered.

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Constant declaration

Constants are declared using the keywordlet the following syntax:

let constantName = <initial value>

The following is a simple instance of Swift program constants:

import Cocoa

let constA = 42
print(constA)

The above program execution results:

42

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Type annotation

When you declare a variable or constant can add type annotations (type annotation), illustrate the type of constant or variable to store the value. If you want to add a type annotation, you need to add a colon and space after constant or variable name, and then add the type name.

var constantName:<data type> = <optional initial value>

The following is a simple example to demonstrate the Swift is in constant use type annotations. Note that the initial value must be constant defines:

import Cocoa

let constA = 42
print(constA)

let constB:Float = 3.14159

print(constB)

The above program execution results:

42
3.14159

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Named Constant

Named constants can consist of letters, numbers and underscores.

The constant need to start with a letter or an underscore.

Swift is a case-sensitive language, so uppercase and lowercase letters are not the same.

You can also use a simple constant name Unicode characters following examples:

import Cocoa

let _const = "Hello, Swift!"
print(_const)

let 你好 = "你好世界"
print(你好)

The above program execution results:

Hello, Swift!
你好世界

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Constant output

Variables and constants can use print (swift 2 replaces the print println) function to output.

Parentheses can be used in the string with a backslash to insert constants as examples:

import Cocoa

let name = "本教程"
let site = "http://www.w3write.com"

print("\(name)的官网地址为：\(site)")

The above program execution results:

本教程的官网地址为：http://www.w3write.com