Random

In Swift 5.8, we compute random Ints with a Foundation function. With arc4random, we can begin a random sequence of numbers. Our program will begin a different sequence each time.

Arc4random is a good choice for random numbers in many Swift programs. But it is not sufficient for some—it is a pseudo-random number generator.

A first example

This example uses the arc4random function. In Xcode you can scroll through a list of functions by typing a few characters like "ar."

import Foundation

// Use infinite "repeat while true" loop.
repeat {
    // Get random number with arc4random.
    let number = arc4random()
    print("The computer selected: \(number)")

    // Check for multiple of 10.
    if number % 10 == 0 {
        print("Divisible by 10, stopping loop.")
        break
    }

    if number % 5 == 0 {
        print("Divisible by 5, you are a winner.")
    }

} while true
The computer selected: 1580707251
The computer selected: 2169372518
The computer selected: 2188614733
The computer selected: 2102187726
The computer selected: 1259434845
Divisible by 5, you are a winner.
The computer selected: 4203979483
The computer selected: 3751678511
The computer selected: 1143995553
The computer selected: 1399438296
The computer selected: 4189143210
Divisible by 10, stopping loop.

Arc4random, seed

With arc4random, a different sequence is generated each time a program is run. No special seed value must be specified.

import Foundation

// With arc4random we do not need to seed the random number generator.
// ... A difference sequence is generated each time.
print("Test")
for _ in 0...3 {
    print(arc4random())
}
Test
2350561563
3189423288
1041162380
2422311100
(Second run)
Test
1179004133
1484905321
2378084349
2120303966

With helpful Foundation methods, we generate random numbers in Swift. Arc4random is used for best pseudo-random results. It does not need a special seed.