BigInt example with changes.

BigInt4.swift

struct BigInt {

    var value: String

    func multiply(right: String) -> String {
        // We'll change this line to use `value`
        var leftCharacterArray = value.characters.reversed().map { Int(String($0))! }
        var rightCharacterArray = right.characters.reversed().map { Int(String($0))! }
    ...


// Now we can do this
let int1 = BigInt(value: "34")  
let int2 = BigInt(value: "45")  
let product = int1.multiply(int2.value)