Generate random number of certain amount of digits

Question

Hy,

I have a very Basic Question which is :

How can i create a random number with 20 digits no floats no negatives (basically an Int) in Swift ?

Than

Answer 1

Swift 4 version of Unome's validate response plus :

• Guard it against overflow and 0 digit number

• Adding support for Linux's device because "arc4random*" functions don't exit

With linux device don't forgot to do

#if os(Linux)
    srandom(UInt32(time(nil)))
#endif

only once before calling random.

/// This function generate a random number of type Int with the given digits number
///
/// - Parameter digit: the number of digit
/// - Returns: the ramdom generate number or nil if wrong parameter
func randomNumber(with digit: Int) -> Int? {

    guard 0 < digit, digit < 20 else { // 0 digit number don't exist and 20 digit Int are to big
        return nil
    }

    /// The final ramdom generate Int
    var finalNumber : Int = 0;

    for i in 1...digit {

        /// The new generated number which will be add to the final number
        var randomOperator : Int = 0

        repeat {
            #if os(Linux)
                randomOperator = Int(random() % 9) * Int(powf(10, Float(i - 1)))
            #else
                randomOperator = Int(arc4random_uniform(9)) * Int(powf(10, Float(i - 1)))
            #endif

        } while Double(randomOperator + finalNumber) > Double(Int.max) // Verification to be sure to don't overflow Int max size

        finalNumber += randomOperator
    }

    return finalNumber
}