Category: 01. Basic

Swift Multiple Variables

Declare multiple variables or constants on one line when they share a type.

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Multiple Variables Declared

Declaring multiple variables or constants on one line is only recommended if it stays easy to read.

Example

var x = 1, y = 2, z = 3
let a = 10, b = 20
print(x, y, z, a, b)

This example declares multiple variables and constants on one line.

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With Type Annotations

Use explicit types when inference could be ambiguous or to document intent.

Example

var i: Int = 1, j: Int = 2
let firstName: String = "Robin", lastName: String = "Refsnes"
print(i + j, firstName, lastName)

This example declares multiple variables and constants on one line.

Swift Print Variables

Print values with concatenation or string interpolation.

Use \(value) to insert values. You can set a separator and a terminator.

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Concatenation and Interpolation

Use concatenation to combine strings and interpolate to embed values inside strings.

Example

let first = "Hello"
let second = "Swift"
// Concatenation
print(first + ", " + second)
// Interpolation
print("\(first), \(second)")

let a = 2, b = 3
print("a = \(a), b = \(b), sum = \(a + b)")

This example shows concatenation and interpolation.

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Custom Separator and Terminator

Set a separator between items and a terminator at the end.

Example

let a = 1, b = 2, c = 3
print(a, b, c, separator: ", ", terminator: "; ")
print("done")  // prints on the same line after a semicolon

This example sets a comma-space separator and a semicolon terminator.

Swift Variables

Declare constants with let, variables with var, and use type inference or annotations as needed.

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Constants and Variables

Declare constants with let and variables with var.

Constants cannot be reassigned.

Example

let constant = 10
var counter = 0
counter += 1
// constant = 12 // Error if uncommented
print(constant, counter)

This example shows that var can change while let cannot.

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Swift Type Inference

Swift infers types automatically when possible, but you can also use annotations for clarity.

Example

let x = 10
let y: Int = 20
print(x, y)

This example shows that Swift infers types automatically when possible, but you can also use annotations for clarity.

Swift Data Types will be covered in more detail in the Swift Data Types chapter.

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Optionals

Use ? to declare values that may be nil.

Example

var nickname: String? = nil
nickname = "KJ"
print(nickname ?? "none")

This example shows an optional that may be nil.

Swift Comments

Use comments to explain code.

Swift supports single-line, multi-line (nestable), and documentation comments.

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Single-line and Multi-line

Use // for single-line comments and /* ... */ for multi-line comments.

Example

// This is a single-line comment
print("Hello")

/* This is a
   multi-line comment */
print("Swift")

/* Nested comments are allowed:
  /* inner */
*/

This example shows single- and multi-line comments.

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Documentation Comments

Use /// before declarations to generate documentation, e.g. for functions, types, and properties.

Documentation comments can include parameters, return values, and more.

They differ from regular comments in that they are processed by the compiler and can be used to generate documentation.

Example

/// Returns the sum of two integers.
/// - Parameters: a, b
func add(_ a: Int, _ b: Int) -> Int { a + b }
print(add(2, 3))

This example uses triple-slash comments to document a function.

Swift Number Output

Print numeric values with print() and format using interpolation or format styles.

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Printing Numbers

Print values directly or embed them using string interpolation with \(value).

Example

let a = 7, b = 3
print(a, b)                 // space-separated by default
print("a=\(a), b=\(b)")     // interpolation
print("sum = \(a + b)")     // inline math

This example prints numbers directly and via string interpolation, including inline addition.

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Math Functions

Common functions like abs, min, and max help compute numeric results.

• abs(x) returns the absolute value of x.
• min(x, y) returns the smaller of x and y.
• max(x, y) returns the larger of x and y.

Example

let x = -7
print(abs(x))          // 7
print(min(3, 8))       // 3
print(max(3, 8))       // 8

This example shows absolute value, minimum, and maximum functions.

Use print() to write text and values to output.

Use string interpolation to combine values.

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Print Text

Use print() to write text.

Interpolate values with \(expr).

Example

print("Hello, Swift!")
let name = "Kai"
print("Hello, \(name)!")

let a = 2, b = 3
print("Total: \(a + b)")

This example prints text and uses string interpolation to include values.

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Print Without Newline

Use the terminator parameter to avoid a trailing newline.

Example

for n in 1...3 {
  print(n, terminator: " ") // prints on one line
}
print("done")

This example prints numbers on a single line by setting terminator to a space, then prints done on the next line.

Swift Statements

Swift code is built from statements such as declarations, expressions, and control flow (if, switch, loops).

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Expression & Declaration Statements

Declarations introduce names (like variables and constants).

Expression statements evaluate an expression, such as a function call.

Example

let x = 2  // declaration
print(x)    // expression statement

Learn Swift basics: variables, types, string interpolation, and simple functions.

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Basics

Lets look at some basic Swift syntax:

• Constants/variables: Use let (constant) and var (variable).
• Types: Common types include Int, Double, Bool, String.
• Type inference: The compiler infers types from initial values.

Example

let greeting = "Hello"
var name = "Swift"
print(greeting + ", " + name)

let pi: Double = 3.14159
var count: Int = 3
print("pi = \(pi), count = \(count)")

Note: Unlike some other languages, in Swift let is used for constants and var for variables.

Example explained

• let creates an immutable constant; var creates a mutable variable.
• Type annotation is optional; here we annotate Double and Int.
• String interpolation: \(expr) inserts values into strings.

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String Interpolation

String interpolation is a way to embed expressions inside string literals for formatting.

In swift string interpolation is done using \(expr).

The most common and simple way to use string interpolation is to embed variable names inside string literals.

Example

let greeting = "Hello"
var name = "Swift"
print("\(greeting), \(name)!")

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Install the Swift toolchain and run your first “Hello, Swift!” program from the terminal or Xcode.

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Install Swift

Swift can be installed on macOS, Windows, and Linux.

• macOS (Xcode): Install Xcode from the App Store. Xcode includes the Swift compiler, SDKs, and tools.
• macOS (Command line): Install the Swift toolchain, then run swift --version.
• Windows/Linux: Install the platform toolchain from swift.org/install and ensure swift is on your PATH.

Check install: Run swift --version in a terminal.

You should see the Swift version and target.

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Hello World

Swift can be run from the terminal or Xcode.

Syntax: print("Hello, Swift!"); run with swift main.swift (or your toolchain’s run command).

Example

main.swift

print("Hello, Swift!")

Example explained

• main.swift: A Swift file; the top-level print executes when run.
• print: Writes text to standard output. Strings use double quotes.

Swift is a modern, fast, and safe language for building apps across Apple platforms and beyond.

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What is Swift?

Swift is a modern, fast, and safe programming language created by Apple.

Use it to build apps for iPhone, iPad, Mac, Apple Watch, and Apple TV.

You can also run Swift on servers (Linux, Windows, macOS).

Swift helps you write correct and efficient code with type inference, optionals, value types, and protocol-oriented programming.

Example

print("Hello, Swift!")

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Why Use Swift?

Swift focuses on safety and speed.

Features like optionals, value types, and generics help you avoid bugs and keep code clear.

• Great for iPhone/iPad, Mac, Apple Watch, and Apple TV development
• Open source and available on multiple platforms
• Expressive syntax, optionals to model absence, and value types for predictable behavior
• Vibrant ecosystem and first-class tooling in Xcode

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Swift History

A brief timeline of important Swift releases and milestones.

• 2014: Swift 1.0 announced at WWDC as a modern successor to Objective-C
• 2015: Swift became open source at swift.org, with Linux support
• 2019: Swift 5 introduced ABI stability on Apple platforms
• 2021: Swift 5.5 added structured concurrency (async/await, Task, actor)
• Today: Used across iOS, macOS, and server-side Swift

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Mac and Xcode for iOS Development

If your goal is to build and run iOS apps, you should use a Mac with Xcode.

• Xcode includes iOS SDKs, simulators, Interface Builder, and signing tools.
• You can learn Swift on Windows or Linux and in the browser, but building and running iOS apps requires a Mac.
• To ship to TestFlight or the App Store, you need an Apple Developer account.