cs193p – Assignment #1 Extra Task #3

Make one of your operation buttons be “generate a random double-precision floating point number between 0 and 1”. This operation button is not a constant (since it changes each time you invoke it). Nor is it a unary operation (since it does not operate on anything). Probably the easiest way to generate a random number in iOS is the global Swift function arc4random() which generates a random number between 0 and the largest possible 32-bit integer (UInt32.max). You’ll have to get to double precision floating point number from there, of course.

Change one of the buttons in story board:

Add an operation without operands to the the calculator model:

    private enum Operation {
        ...
        case nullaryOperation(() -> Double, String)
        ...
    }

The “random” operation returns the function generating the random number as well as a string for its description:

private let operations: Dictionary<String,Operation> = [
    ...        
    "rand" : Operation.nullaryOperation(
        { Double(arc4random()) / Double(UInt32.max) }, 
        "rand()"
    )
]

… which are used to calculate the result and the description:

    mutating func performOperation(_ symbol: String) {
                ...
            case .nullaryOperation(let function, let description):
                accumulator = (function(), description)
            ...
    }

The complete code for the assignment #1 extra task #3 is available on GitHub.