9.24.1. Create a string #

You can use the literal amount of a string or String class to create a string:

import Cocoa

// Using string literals
var stringA = "Hello, World!"
print( stringA )

// String instantiate
var stringB = String("Hello, World!")
print( stringB )

The output of the above program execution is as follows:

Hello, World!
Hello, World!

9.24.2. Empty string #

You can use empty string literals to assign values to variables or initialize a String class to initially value an empty string. We can use string properties isEmpty to determine whether the string is empty:

import Cocoa

// Create an empty string using string literals
var stringA = ""

if stringA.isEmpty {
   print( "StringA is empty" )
} else {
   print( "StringA is not empty" )
}

// Instantiating the String class to create an empty string
let stringB = String()

if stringB.isEmpty {
   print( "stringB is empty" )
} else {
   print( "stringB is not empty" )
}

The output of the above program execution is as follows:

stringA is empty
stringB is empty

9.24.3. String constant #

You can assign a string to a variable or constant. Variables are modifiable and constants are immutable.

import Cocoa

// stringA can be modified
var stringA = "Rookie Tutorial："
stringA += "http://www.runoob.com"
print( stringA )

// stringB can not be modified
let stringB = String("Rookie Tutorial：")
stringB += "http://www.runoob.com"
print( stringB )

The output of the above program will report an error, because stringB being a constant cannot be modified:

error: left side of mutating operator isn't mutable: 'stringB' is a 'let' constant
stringB += "http://www.runoob.com"

9.24.4. Insert a value into a string #

String interpolation is a way to build new strings that can include constants, variables, literals, and expressions. Each item of the literal amount of the string you insert is in parentheses prefixed with a backslash:

import Cocoa

var varA   = 20
let constA = 100
var varC:Float = 20.0

var stringA = "\(varA) by \(constA) equal to \(varC * 100)"
print( stringA )

The output of the above program execution is as follows:

20 by 100 equal to 2000.0

9.24.5. String concatenation #

Strings can be concatenated with the + sign. Examples are as follows:

import Cocoa

let constA = "Rookie Tutorial："
let constB = "http://www.runoob.com"

var stringA = constA + constB

print( stringA )

The output of the above program execution is as follows:

Rookie Tutorial：http://www.runoob.com

9.24.6. String length #

String length using String.count property, an example is as follows:

The Swift 3 version uses the String.characters.count

import Cocoa

var varA   = "www.runoob.com"

print( "\(varA), the length is \(varA.count)" )

The output of the above program execution is as follows:

www.runoob.com, the length is 14

9.24.7. String comparison #

You can use == to compare whether two strings are equal:

import Cocoa

var varA   = "Hello, Swift!"
var varB   = "Hello, World!"

if varA == varB {
   print( "\(varA) and \(varB) is equal" )
} else {
   print( "\(varA) and \(varB) is not equal" )
}

The output of the above program execution is as follows:

Hello, Swift! and Hello, World! is unequal

9.24.8. Unicode String #

Unicode is an international standard for text encoding, Swift String the type is based on Unicode it was built. You can iterate through the string. UTF-8 and UTF-16 an example of the code is as follows:

import Cocoa

var unicodeString   = "Rookie Tutorial"

print("UTF-8 code: ")
for code in unicodeString.utf8 {
   print("\(code) ")
}

print("\n")

print("UTF-16 code: ")
for code in unicodeString.utf16 {
   print("\(code) ")
}

The output of the above program execution is as follows:

UTF-8 code:
232
143
156
233
184
159
230
149
153
231
168
139
UTF-16 code:
33756
40479
25945
31243

9.24.9. String functions and operators #

Swift supports the following string functions and operators:

let myString: String = "256"
let myInt: Int? = Int(myString)