How to generate a big number of specific length in Swift?.md

Problem

Need a big random number of a specific length in Swift.

Environment

N/A

How you fix it

=> This problem could be solved using the .random() function available in Swift but in that case, you need to provide the range. If you need a number with 19 digits you need to provide an upper limit of range with 19 digits number which seems a hassle. I devised two solutions for this problem which I am sharing below

Solution

1. Use UUID Strings and filter out all the numbers until you get the desired length
2. Start from an empty and attach random digits from the range 1-9 until you get the desired length. But please note in this case your loop will iterate n times where n = digits lenght.

1) Using UUID Strings

import Foundation

func generateBigRandomNumber(digits: Int = 19) -> UInt64 {
    var randomDigits = ""

    while randomDigits.count < digits {
        let uuid = UUID().uuidString.replacingOccurrences(of: "-", with: "")
        randomDigits += uuid.filter { $0.isNumber }
    }

    randomDigits = String(randomDigits.prefix(digits))
    return UInt64(randomDigits) ?? 0
}

1) Using Strings and adding 1 random digit at a time

import Foundation

func generateBigRandomNumberOf(digits: Int) -> String {
    
    var bigRandomNumber = String()
    for _ in 1...digits {
       bigRandomNumber += "\(Int.random(in: 1...9))"
    }
    return bigRandomNumber
}