                         outputArray.removeAtIndex(i - 1)
                     }
                 default:
-                    println("Unrecognized operator.")
+                    outputArray.removeAll(keepCapacity: false)
+                    outputArray.append("An unknown error has occured.")
+                    return outputArray
                 }
                 i = 0
             } else {

                    outputArray[i] = "\(results)"
                    outputArray.removeAtIndex(i - 2)
                    outputArray.removeAtIndex(i - 2)
                    //                case "!":
                case "%":
                    if nums >= 1 {
                        var tmp = (outputArray[i - 1] as NSString).doubleValue / 100

        }
        return outputArray
    }
    
}
