private void HandleOperatorInput(char key) { if (operation != null && isResultUpdated) { result = operation.Operate(result, Convert.ToDouble(operand.ToString())); } else { result = Convert.ToDouble(operand.ToString()); } operation = operatorFactory.GetOperation(key); operand.Clear().Append(result.ToString()); isOperandConsumed = true; isResultUpdated = true; }