How to convert a binary to decimal in Swift?

Question

I am looking for a simple way to convert a binary number in decimal in Swift. For example, \"10\" in binary becomes \"2\" in decimal.

Thanks,

Answer 1

There may be a built-in to do this, but writing the code yourself isn't hard:

func parseBinary(binary: String) -> Int? {
    var result: Int = 0

    for digit in binary {
        switch(digit) {
            case "0": result = result * 2
            case "1": result = result * 2 + 1
            default: return nil
        }
    }
    return result
}

The function returns an (optional) Int. If you want to get a string instead, you can do the following:

String(parseBinary("10101")!)
-> "21"

Note the forced unwrapping (!) If the string you provide contains anything other than 0's or 1's, the function returns nil and this expression will blow up.

Or, taking a cue from Leonardo, you can build this as an extension to string:

extension String {
    func asBinary() -> Int? {
        var result: Int = 0

        for digit in self {
            switch(digit) {
                case "0": result = result * 2
                case "1": result = result * 2 + 1
                default: return nil
            }
        }
        return result
    }
}

"101".asBinary()!
-> 5