Lesson 3Swift Basics

Data Types

Swift Data Types

Every variable in Swift has a specific type that determines what kind of data it can hold. Swift is a type-safe language!

Common Data Types

Int

Whole numbers: 1, 42, -100

Double

Decimals: 3.14, -0.5, 99.99

String

Text: "Hello", "Swift"

Bool

True or False values

Type Inference

Swift is smart! It can figure out the type automatically based on the value you assign:

  • 42 → Int
  • 3.14 → Double
  • "Hi" → String
  • true → Bool

Type Annotations

You can explicitly specify the type using a colon:

let age: Int = 12
main.swift
// Integer - whole numbers
let age: Int = 12
var score: Int = 100
let negative: Int = -50

// Double - decimal numbers (more precision)
let pi: Double = 3.14159265359
let price: Double = 9.99

// Float - decimal numbers (less precision)
let temperature: Float = 98.6

// String - text
let name: String = "Swift"
let message: String = "Hello, World!"

// Bool - true or false
let isStudent: Bool = true
let gameOver: Bool = false

// Type inference - Swift figures it out!
let inferredInt = 42        // Int
let inferredDouble = 3.14   // Double
let inferredString = "Hi"   // String
let inferredBool = true     // Bool

// Check the type
print(type(of: inferredInt))    // Int
print(type(of: inferredDouble)) // Double

Try It Yourself!

Create variables for: your age (Int), height in meters (Double), your name (String), and whether you like coding (Bool)!