S版照你指导的修改了 最终结果这样
程序代码：
程序代码：frmMain = CREATEOBJECT("C_Form")
frmMain.show
READ events
RETURN
DEFINE CLASS C_Form as Form
caption = "简单计算器"
width = 600
height = 400
autocenter = .T.
ADD OBJECT Label1 as label WITH caption="第一个数", Width=60,height=25,Top=100,Left=50
ADD OBJECT Label2 as label WITH caption="第二个数", Width=60,height=25,Top=ThisForm.Label1.Top,Left=ThisForm.Width/2
ADD OBJECT Label3 as label WITH caption= "最终结果",Width=60,height=25
ADD OBJECT Text1 as TextBox WITH value="",Width=100,height=25,Top=ThisForm.Label1.Top,Left=ThisForm.Label1.Left+ThisForm.Label1.Width+5
ADD OBJECT Text2 as TextBox WITH value="",Width=100,height=25,Top=ThisForm.Label1.Top,Left =ThisForm.Label2.Left+ThisForm.Label2.Width+5
ADD OBJECT Text3 as TextBox WITH value="",Width=100,height=25
ADD OBJECT ComboBox1 as ComboBox WITH caption = "计算方式", Height = 20, Width = 50
PROCEDURE init
WITH ThisForm.Label3
.Top = ThisForm.Label1.Top + ThisForm.Label1.Height + 50
.Left = ThisForm.Width / 2 - .Width
ENDWITH
WITH ThisForm.Text3
.Top = ThisForm.Label3.Top
.Left = ThisForm.Label3.Left + ThisForm.Label3.Width + 5
ENDWITH
WITH Top = ThisForm.Label3.Top
.Left = ThisForm.Label3.Left - .Width - 5
.style = 0
.inputmask = .displayvalue
.rowsource=[+,-,*,/] &&
.rowsourcetype=1 &&
.ColumnCount = 1
.ColumnLines = .F.
ENDWITH
ENDPROC
PROCEDURE destroy
CLEAR EVENTS
ENDPROC
PROCEDURE combobox1.interactivechange
LOCAL v as Double
WITH ThisForm
DO CASE
CASE = '+'
v = VAL(.Text1.Value) + VAL(.Text2.Value)
CASE = '-'
v = VAL(.Text1.Value) - VAL(.Text2.Value)
CASE = '*'
v = VAL(.Text1.Value) * VAL(.Text2.Value)
CASE = '/'
IF VAL(.Text2.Value) != 0
v = VAL(.Text1.Value) / VAL(.Text2.Value)
ELSE
MESSAGEBOX("零做除数是非法的", 0)
return
ENDIF
OTHERWISE
MESSAGEBOX("错误的计算方法", 0)
return
ENDCASE
.Text3.Value = str(v,10, 2)
ENDWITH
ENDPROC
ENDDEFINE非常感谢你的指教 
梅尚程荀
马谭杨奚
