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

Step 1

First of all we need an extension of Int to generate a random number in a range.

extension Int {
    init(_ range: Range<Int> ) {
        let delta = range.startIndex < 0 ? abs(range.startIndex) : 0
        let min = UInt32(range.startIndex + delta)
        let max = UInt32(range.endIndex   + delta)
        self.init(Int(min + arc4random_uniform(max - min)) - delta)
    }
}

This can be used this way:

Int(0...9) // 4 or 1 or 1...
Int(10...99) // 90 or 33 or 11
Int(100...999) // 200 or 333 or 893

Step 2

Now we need a function that receive the number of digits requested, calculates the range of the random number and finally does invoke the new initializer of Int.

func random(digits:Int) -> Int {
    let min = Int(pow(Double(10), Double(digits-1))) - 1
    let max = Int(pow(Double(10), Double(digits))) - 1
    return Int(min...max)
}

Test

random(1) // 8
random(2) // 12
random(3) // 829
random(4) // 2374