Why does this piece of code gives error and couldn't print result?-CodePudding

Can anyone point out the problem with the code below? I couldn't get it run properly in Xcode playground, any help would be greatly appreciated.

func calculator(a:Int, b:Int) {
  let a = Int(readLine()!)! //First input
  let b = Int(readLine()!)! //Second input

  add(n1: a, n2: b)
  subtract(n1: a, n2: b)
  multiply(n1: a, n2: b)
  divide(n1: a, n2: b)
  
}

//Write your code below this line to make the above function calls work.

func add(n1:Int, n2:Int){
    print(n1 n2)
}

func subtract(n1:Int, n2:Int){
    print(n1-n2)
}
func multiply(n1:Int, n2:Int){
    print(n1*n2)
}
func divide(n1:Int, n2:Int){
    let a1 = Double(n1)
    let a2 = Double(n2)
    print(a1 / a2)
}


calculator(a:3, b:4)

Error:

error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0). __lldb_expr_1/MyPlayground.playground:4: Fatal error: Unexpectedly found nil while unwrapping an Optional value

Expect it to simply print result of add, subtract, multiply, and divide.

CodePudding user response：

The error was that you created useless constants in which you did not pass values. The correct way to do this is to pass a value in the parameters of a function when you call it

func calculator(a:Int, b:Int) {
      
      add(n1: a, n2: b)
      subtract(n1: a, n2: b)
      multiply(n1: a, n2: b)
      divide(n1: a, n2: b)
      
    }
    
    //Write your code below this line to make the above function calls work.
    
    func add(n1:Int, n2:Int){
        print(n1 n2)
    }
    
    func subtract(n1:Int, n2:Int){
        print(n1-n2)
    }
    func multiply(n1:Int, n2:Int){
        print(n1*n2)
    }
    func divide(n1:Int, n2:Int){
        let a1 = Double(n1)
        let a2 = Double(n2)
        print(a1 / a2)
    }