A couple functions for doing Integer to Binary Conversion in swift.

intToBinary.swift

import UIKit

func intToBin(num: Int, padding: Bool = true ) -> String {
    var binString = String(num, radix:2)
    if padding {
        binString = padStringTo4DigitChunks(binString)
    }
    return binString
}

func padStringTo4DigitChunks(binString:String) -> String {
    //hexStringWill alwasy be "1001" easily stored as ascii
    let numToPad = binString.lengthOfBytesUsingEncoding(NSASCIIStringEncoding) % 4
    switch numToPad {
    case 1: return "000" + binString
    case 2: return "00" + binString
    case 3: return "0" + binString
    default: return binString //default to no padding
    }
}

intToBin(1, padding: true) // "0001"
intToBin(1) // "1"
intToBin(5, padding: true) // "0101"

intToBin(8, padding: true) // 1000
intToBin(15, padding: true) // 1111
intToBin(16) // 1_0000
intToBin(16, padding: true) //since 16 has 5 binary digits 0001_0000