1 Operation operation = new Operation();
 2                 switch (cmbCountWay.SelectedItem.ToString().Trim())
 3                 {
 4                     case "+":
 5                         operation = new OperationAdd();
 6                         break;
 7                     case "-":
 8                         operation = new OperationSubtraction();
 9                         break;
10                     case "*":
11                         operation = new OperationMultiplication();
12                         break;
13                     case "/":
14                         operation = new OperationDivision();
15                         break;
16                     default:
17                         break;
18                 }
19                 //进行计算
20                 operation.FirstNum = double.Parse(txtFirstNum.Text.Trim());
21                 operation.SecondNum = double.Parse(txtSecondNum.Text.Trim());
22                 double result = operation.GetCount();
23                 this.txtResult.Text = result.ToString();

 public class OperatorFactory{public static Operator CreatOperator(string oper){Operator calc = null;switch (oper){case"+":calc = new Add();break;case"-":calc = new Sum();break;case"*":calc = new Mul();break;case"/":calc = new Div();break;}return calc;}}

 private void btnCount_Click(object sender, EventArgs e){int numLeft = Convert.ToInt32(txtNumLeft.Text);int numRight = Convert.ToInt32(txtNumRight.Text);string oper = cmbOperator.SelectedItem.ToString();Operator calc = OperatorFactory.CreatOperator(oper);try{calc.NumLeft = numLeft;calc.NumRight = numRight;txtResult.Text = calc.Operation().ToString();}catch (Exception ex){MessageBox.Show(ex.Message);}}