逆波兰表达式在VB中编程？？？

[lihuanmei]

Problem :逆波兰表达式

逆波兰表达式是一种把运算符前置的算术表达式，例如普通的表达式2 + 3的逆波兰表示法为+ 2 3。逆波兰表达式的优点是运算符之间不必有优先级关系，也不必用括号改变运算次序，例如(2 + 3) * 4的逆波兰表示法为* + 2 3 4。本题求解逆波兰表达式的值，其中运算符包括+ - * /四个。
输入为一行，其中运算符和运算数之间都用空格分隔，运算数是浮点数。
输出为一行，表达式的值。
可直接用printf("%f\n", v)输出表达式的值v。
可使用atof(str)把字符串转换为一个double类型的浮点数。atof定义在math.h中。
此题可使用函数递归调用的方法求解。


请问各位大侠：如何编程啊？？

[Tiger_Zhao]

sub main()
    debug.print f("*+234",1)
end sub
function f(byval exp as string, byref i as long) as double
    dim ch as string, a as double, b as double
    ch = mid$(exp,i,1)
    i = i+1
    select case ch
        case "+"
            a = f(exp, i)
            b = f(exp, i)
            f = a + b        
        case "-" '参考 case "+"
        case "*" '参考 case "+"
        case "/" '参考 case "+"
        case else
            f = val(ch)
    end select
end function

[mokton]

学习呀

[zzyong00]

Dim symbol() As String, data() As String

Private Sub Command1_Click()
ReDim symbol(0), data(0)
Dim s As String
Analysis " / * + 2 3 4 5"
Debug.Print Calc(s)
End Sub

Public Function Analysis(ByVal exp As String) As String
    Dim strCh As String
    Dim i As Integer
    For i = 1 To Len(exp)
        strCh = Mid$(exp, i, 1)
        If strCh <> " " Then
            If strCh = "+" Or strCh = "-" Or strCh = "*" Or strCh = "/" Then
                symbol(UBound(symbol)) = strCh
                ReDim Preserve symbol(UBound(symbol) + 1)
            ElseIf IsNumeric(strCh) Then
                data(UBound(data)) = strCh
                ReDim Preserve data(UBound(data) + 1)
            Else
                Analysis = "error"
            End If
        End If
    Next
End Function

Public Function Calc(ByVal ErrMsg As String) As Double
    On Error GoTo ToExit '´ò¿ª´íÎóÏÝÚå
    '------------------------------------------------
    Dim i As Integer, intPos As Integer
    Dim result As Double
    For i = UBound(symbol) - 1 To 0 Step -1
        Select Case symbol(i)
        
            Case "+"
                If pos = 0 Then
                    result = Val(data(pos)) + Val(data(pos + 1))
                    pos = pos + 1
                Else
                    result = result + Val(data(pos + 1))
                    pos = pos + 1
                End If
            Case "-"
                If pos = 0 Then
                    result = Val(data(pos)) - Val(data(pos + 1))
                    pos = pos + 1
                Else
                    result = result - Val(data(pos + 1))
                    pos = pos + 1
                End If
            Case "*"
                If pos = 0 Then
                    result = Val(data(pos)) * Val(data(pos + 1))
                    pos = pos + 1
                Else
                    result = result * Val(data(pos + 1))
                    pos = pos + 1
                End If
            Case "/"
                If pos = 0 Then
                    result = Val(data(pos)) / Val(data(pos + 1))
                    pos = pos + 1
                Else
                    result = result / Val(data(pos + 1))
                    pos = pos + 1
                End If
        End Select
    Next
    Calc = result
    '------------------------------------------------
    Exit Function
    '----------------
ToExit:
ErrMsg = Err.Number & ":" & Err.Description
End Function