How to calculate the 21! (21 factorial) in swift?

Question

I am making fuction that calculate factorial in swift. like this

func factorial(factorialNumber: UInt64) -> UInt64 {
    if factorialNumber == 0 {
                


        

Answer 1

If you are willing to give up precision you can use a Double to roughly calculate factorials up to 170:

func factorial(_ n: Int) -> Double {
    if n == 0 {
        return 1
    }
    var a: Double = 1
    for i in 1...n {
        a *= Double(i)
    }
    return a
}

If not, use a big integer library.