Online Swift Compiler – Instantly Run Swift Code in Your Browser

Write and execute Swift code in real time with our free online Swift compiler. Perfect for iOS developers and Swift learners — it's fast, easy, and works right in your browser.

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💡 Swift Basics Guide for Beginners

1. Declaring Variables and Constants

Use var for variables and let for constants in Swift.

var age = 30
let pi = 3.14159
var name = "Alice"
let isActive = true

// Constants cannot be reassigned
// pi = 3.14 // ❌ Error

2. Conditionals (if / switch)

Use if, else if, else for logic, and switch for multiple branches.

let number = 2
if number == 1 {
    print("One")
} else if number == 2 {
    print("Two")
} else {
    print("Other")
}

switch number {
case 1:
    print("One")
case 2:
    print("Two")
default:
    print("Other")
}

3. Loops

Swift supports for-in, while, and repeat-while loops.

for i in 0..<3 {
    print(i)
}

var n = 3
while n > 0 {
    print(n)
    n -= 1
}

4. Arrays

Arrays store ordered collections of values.

var numbers = [10, 20, 30]
print(numbers[1])

5. Array Manipulation

Use array methods like append and removeLast.

var nums = [1, 2, 3]
nums.append(4)
nums.removeLast()

for n in nums {
    print(n)
}

6. Console Input/Output

Use print() for output. Input requires additional work in Swift Playgrounds or Xcode.

let name = "Alice"
print("Hello, \(name)")

7. Functions

Define reusable functions with parameters and return values.

func add(a: Int, b: Int) -> Int {
    return a + b
}

print(add(a: 3, b: 4))

8. Dictionaries

Dictionaries store key-value pairs.

var ages = ["Alice": 30]
print(ages["Alice"] ?? 0)

9. Error Handling

Swift uses do-catch for error handling.

enum MyError: Error {
    case runtimeError(String)
}

do {
    throw MyError.runtimeError("Something went wrong")
} catch let error {
    print(error)
}

10. File I/O

Swift uses FileManager or String methods for file I/O.

let text = "Hello File"
try text.write(toFile: "file.txt", atomically: true, encoding: .utf8)
let content = try String(contentsOfFile: "file.txt")
print(content)

11. String Manipulation

Use methods like count, contains, uppercased(), etc.

let text = "Hello World"
print(text.count)
print(text.contains("World"))
print(text.uppercased())

12. Classes & Objects

Swift supports OOP using class and init.

class Person {
    var name: String
    init(name: String) {
        self.name = name
    }
    func greet() {
        print("Hi, I'm \(name)")
    }
}

let p = Person(name: "Alice")
p.greet()

13. Optionals

Swift uses ? and ! to handle optional values.

var name: String? = "Alice"
print(name ?? "Unknown")

if let unwrappedName = name {
    print(unwrappedName)
}