Parameters

// BASIC PARAMETERS
func greet(name: String) {
    print("Hello, \(name)!")
}
greet(name: "Alice")  // name is required

// MULTIPLE PARAMETERS
func describe(name: String, age: Int, hobby: String) {
    print("\(name) is \(age) and loves \(hobby)")
}
describe(name: "Bob", age: 13, hobby: "coding")

// PARAMETER ORDER MATTERS!
// Must provide arguments in the same order as defined

// EXTERNAL AND INTERNAL NAMES
// Swift lets you have two names for each parameter
func greet(person name: String) {
    // 'person' is external (used when calling)
    // 'name' is internal (used inside function)
    print("Hello, \(name)!")
}
greet(person: "Charlie")

// OMITTING EXTERNAL NAME WITH _
func add(_ a: Int, _ b: Int) -> Int {
    return a + b
}
print(add(5, 3))  // No labels needed!

// DIFFERENT EXTERNAL AND INTERNAL NAMES
func move(from start: Int, to end: Int) {
    print("Moving from \(start) to \(end)")
}
move(from: 0, to: 100)  // Reads like English!

// INOUT PARAMETERS (modifies original value)
func double(_ number: inout Int) {
    number *= 2
}

var myNumber = 5
double(&myNumber)  // Note the & symbol
print(myNumber)    // 10 (original changed!)

// VARIADIC PARAMETERS (accepts any number of values)
func sum(_ numbers: Int...) -> Int {
    var total = 0
    for num in numbers {
        total += num
    }
    return total
}

print(sum(1, 2, 3))        // 6
print(sum(1, 2, 3, 4, 5))  // 15