@Claude31 is mistake, the correct code is this: while(value < 100.0){ if(self.task != nil){ task2 = self.task if(task2!.countOfBytesSent != 0){ value = (round((Double(100.0)/Double(task2!.countOfBytesExpectedToSend)) * Double(task2!.countOfBytesSent)*100)/100) } } }