18032019_1

import Foundation

class Rational: CustomStringConvertible{
    var n:Int
    var d:Int

    init?(numerator n:Int, denominator d:Int){
        if d==0{
            return nil
        }
        self.n = n
        self.d = d
    }

    var description:String{
        return "\(self.n)/\(self.d)"
    }
}

let opR = Rational(numerator: 1, denominator:0)
print(r)

print(opR)

if let r = opR{
    print(r)
}

if opR != nil{
    let r = opR!
    print(r)
}

func calcValue(opR: Rational?) -> Double?{
    if opR == nil
    {
         return nil
    }
    let r = opR!
    return Double(r.n) / Double(r.d)
 }

func calcValue(opR: Rational?) -> Double?{
    guard let r = opR else{
        return nil
    }
    return Double(r.n) / Double(r.d)
}

    let num:Double? = calcValue(opR) ?? 0

    print(num)