Simple use of functions in Swift 5.

Functions.swift

//
// Simple use of functions
//

// basic function
func description() {
    print("Here's Johnny!")
}
description()     // Here's Johnny!


// accepting parameters
func square(number: Int) {
    print(number * number)
}
square(number: 8)     // 64


// returning values
func double(number: Int) -> Int {
    return number * 2
}
print(double(number: 8))     // 16


// default parameters
func user(name: String, hasAccount: Bool = true) {
    if hasAccount {
        print("Welcome back \(name)!")
    } else {
        print("You must register first.")
    }
}
user(name: "Garry")     // Welcome back Garry!


// variadic function
func isEven(numbers: Int...) {
    let check = numbers.filter {$0 % 2 == 0}
    print(check)
}
isEven(numbers: 1, 2, 3, 4, 5, 6)     // [2, 4, 6]


// inout parameters
func add(number: inout Int) {
    number += 10
}
var number = 5
add(number: &number)
print(number)     // 15