Swift — Variables

let and var

// let: immutable constant
let name = "Alice"
let age = 30

// var: mutable variable
var score = 95
score += 5

// Type annotation
let pi: Double = 3.14
var count: Int = 0

Optionals

var nickname: String? = "Ali"
nickname = nil

// Unwrapping
if let nick = nickname {
    print(nick)
} else {
    print("No nickname")
}

// Guard
func process(name: String?) {
    guard let name = name else {
        print("No name")
        return
    }
    print("Processing: \(name)")
}

// Nil coalescing
let display = nickname ?? "Unknown"

// Optional chaining
let upper = nickname?.uppercased()

Type aliases

typealias UserDict = [String: Int]

let ages: UserDict = ["Alice": 30, "Bob": 25]
print(ages)

Tuple

let person = ("Alice", 30)
print(person.0, person.1)

// Named tuple
let (name2, age2) = ("Bob", 25)
print(name2, age2)

Constants and literals

let binary = 0b1010       // 10
let octal = 0o17          // 15
let hex = 0xFF            // 255
let scientific = 1.25e2   // 125.0

Best practices

• Prefer let over var
• Use optionals carefully
• Use guard for early returns
• Use type aliases for clarity

Mini Practice

Write Swift code that:

1. Uses let and var with type inference
2. Demonstrates optional unwrapping with if let
3. Uses guard for early return
4. Creates a type alias

Up Next

In the next lesson, you'll learn about Data Types — the full type system in Swift.