Lesson 10Swift Basics

Type Conversion

Sometimes you need to convert values from one type to another. Swift requires explicit conversion for safety!

Common Conversions

Int → Double

Double(intValue)

Double → Int

Int(doubleValue)

Truncates decimals!

String → Int

Int(stringValue)

Returns Optional!

Int → String

String(intValue)

Important Notes

Int(3.9) gives 3, not 4 (truncates)
Int("hello") returns nil (can't convert)
String to number conversions return Optionals

Safe String Conversion

Use if let to safely convert strings:

if let num = Int("42") { print(num) }

main.swift

// Int to Double
let age: Int = 12
let ageDouble = Double(age)
print(ageDouble) // 12.0

// Double to Int (truncates decimal part)
let price = 9.99
let priceInt = Int(price)
print(priceInt) // 9

let rounded = Int(3.7)
print(rounded) // 3 (not 4!)

// Mixing types requires conversion
let a: Int = 5
let b: Double = 3.14
let result = Double(a) + b
print(result) // 8.14

// String to Int (returns Optional!)
let numberString = "42"
if let number = Int(numberString) {
    print("Converted: \(number)")
} else {
    print("Conversion failed")
}

// Invalid conversion returns nil
let invalid = Int("hello")
print(invalid) // nil

// Int to String
let score = 100
let scoreString = String(score)
print("Score: " + scoreString)

// String to Double
let piString = "3.14159"
if let pi = Double(piString) {
    print("Pi is \(pi)")
}

// Bool to String
let isTrue = true
print(String(isTrue)) // "true"

// Calculate birth year
let currentYear = 2024
let userAge = 12
let birthYear = currentYear - userAge
print("Born in \(birthYear)")

Try It Yourself!

Convert a user's age from a String to an Int, then calculate and print their birth year!

Module Complete!

Congratulations! You've completed the Swift Basics module. Next up: Control Flow!