Swift Data Types

Every value in Swift belongs to a type. A type tells Swift what kind of data you are storing — a number, text, or true/false value. Swift uses types to prevent you from mixing incompatible data accidentally.

The Grocery Bag Analogy

┌─────────────────────────────────────────────────┐
│        Data Types = Different Compartments      │
│                                                 │
│  Int bag     →  holds whole numbers: 1, 42, -7  │
│  Double bag  →  holds decimals: 3.14, 99.9      │
│  String bag  →  holds text: "Hello", "Swift"    │
│  Bool bag    →  holds true or false only        │
│                                                 │
│  You cannot put an apple in the orange bag.     │
│  Swift enforces this rule automatically.        │
└─────────────────────────────────────────────────┘

Int – Whole Numbers

var age: Int = 25
var floors: Int = 12

Int stores whole numbers — positive, negative, or zero. It cannot hold decimals like 3.14.

Double – Decimal Numbers

var price: Double = 49.99
var pi: Double = 3.14159

Double stores numbers with a decimal point. Use it for prices, measurements, and scientific values. Swift also has Float, which is less precise than Double.

String – Text

var greeting: String = "Good morning"
var country: String = "India"

String stores any text — names, messages, and labels. Always wrap String values in double quotes.

Bool – True or False

var isLoggedIn: Bool = true
var hasPaid: Bool = false

Bool holds only two values: true or false. You use it for decisions like "Is the user signed in?"

Character – A Single Letter

var grade: Character = "A"

Character stores exactly one letter or symbol. A String is a sequence of Characters.

Type Inference – Swift Guesses the Type

var score = 100      // Swift infers: Int
var rate = 4.5       // Swift infers: Double
var name = "Priya"   // Swift infers: String
var isActive = true  // Swift infers: Bool

You do not always need to write the type. Swift reads the value and figures it out. This feature is called type inference.

Type Annotation – You Specify the Type

var distance: Double = 10   // forces Double, not Int

When you need precise control, you write the type after a colon. Here, distance becomes a Double even though 10 looks like an integer.

Type Safety – No Mixing Allowed

var quantity: Int = 5
// quantity = "five"   // Error! Cannot assign String to Int

Swift blocks this at compile time. Once a variable has a type, only values of that same type can go into it.

Type Conversion

var total: Int = 10
var discount: Double = 2.5
var result = Double(total) - discount  // 7.5

To combine different types, convert one explicitly. Double(total) turns the integer 10 into 10.0, making the subtraction work correctly.

Quick Reference Table