【原创】VB利用堆栈实现算术表达式计算
本帖最后由 greatbody 于 2013-04-23 10:48:41 编辑 上了数据结构与算法后，我写了一个函数，基于堆栈类实现对表达式的计算
参考我的博客：VB利用堆栈实现算术表达式计算
下面是模块中的代码：
Public opNum As New StackClass
Public opChar As New StackClass
Public Function CalcString(ByVal strIn As String) As String
Dim sTxt As String
Dim strNumFix As String
Dim curChar As String
Dim i As Long
Dim signCount As Long
Dim ops1 As String, ops2 As String, opC As String
'初始化堆栈
opNum.Clear
opChar.Clear
'堆栈初始化结束
sTxt = strIn
For i = 1 To Len(sTxt)
curChar = Mid(sTxt, i, 1)
If IsSymbol(curChar) = True Then
'看看数字预备区有没有
If strNumFix <> "" Then
opNum.Push strNumFix
strNumFix = ""
End If
redo:
If IsHigh(curChar, opChar.Peek) = 1 Then 'if new come char is higher then push it to stack
opChar.Push curChar '如果等级高的控制符，则进入
signCount = signCount + 1
ElseIf IsHigh(curChar, opChar.Peek) = 0 Then
If curChar = "#" And opChar.Peek = "#" Then
opChar.Pop
CalcString = opNum.Pop
Exit Function
End If
ElseIf IsHigh(curChar, opChar.Peek) = -1 Then 'if low then ready to calculate
'判断是不是第一个符号
If signCount = 1 Then '这个符号是刚刚输入#后的那个，无论如何入栈
opChar.Push curChar
signCount = signCount + 1
GoTo nextone
End If
ops2 = opNum.Pop
ops1 = opNum.Pop
opC = opChar.Pop
opNum.Push CStr(Calc(ops1, ops2, opC))
If curChar = ")" And opChar.Peek = "(" Then
opChar.Pop '如果操作数是），就把（弹出来
GoTo moveon
End If
GoTo redo
moveon:
End If
Else '非符号
strNumFix = strNumFix & curChar
End If
nextone:
Next i
End Function
Public Function Calc(ByVal op1 As String, ByVal op2 As String, ByVal options As String) As Double
On Error Resume Next
Calc = 0
Select Case options
Case "+"
Calc = CDbl(op1) + CDbl(op2)
Case "-"
Calc = CDbl(op1) - CDbl(op2)
Case "*"
Calc = CDbl(op1) * CDbl(op2)
Case "/"
Calc = CDbl(op1) / CDbl(op2)
End Select
End Function
Public Function IsHigh(ByVal sNew As String, ByVal sOld As String) As Integer
'1大于，-1小于，0等于
Select Case sNew
Case "+"
Select Case sOld
Case "("
IsHigh = 1
Exit Function
Case "#"
IsHigh = 1
Exit Function
Case Else
IsHigh = -1
Exit Function
End Select
Case "-"
Select Case sOld
Case "("
IsHigh = 1
Exit Function
Case "#"
IsHigh = 1
Exit Function
Case Else
IsHigh = -1
Exit Function
End Select
Case "*"
Select Case sOld
Case "("
IsHigh = 1
Exit Function
Case "#"
IsHigh = 1
Exit Function
Case "+"
IsHigh = 1
Exit Function
Case "-"
IsHigh = 1
Exit Function
Case Else
IsHigh = -1
Exit Function
End Select
Case "/"
Select Case sOld
Case "("
IsHigh = 1
Exit Function
Case "#"
IsHigh = 1
Exit Function
Case "+"
IsHigh = 1
Exit Function
Case "-"
IsHigh = 1
Exit Function
Case Else
IsHigh = -1
Exit Function
End Select
Case "("
Select Case sOld
Case "+"
IsHigh = 1
Exit Function
Case "-"
IsHigh = 1
Exit Function
Case "*"
IsHigh = 1
Exit Function
Case "/"
IsHigh = 1
Exit Function
Case "("
IsHigh = 1
Exit Function
Case Else
IsHigh = -1
Exit Function
End Select
Case ")"
IsHigh = -1
Exit Function
Case ""
IsHigh = -1
Exit Function
Case "#"
Select Case sOld
Case "#"
IsHigh = 0
Exit Function
Case ""
IsHigh = 1
Exit Function
Case "+"
IsHigh = -1
Exit Function
Case "-"
IsHigh = -1
Exit Function
Case "*"
IsHigh = -1
Exit Function
Case "/"
IsHigh = -1
Exit Function
Case ")"
IsHigh = -1
Exit Function
End Select
End Select
End Function
Public Function IsSymbol(ByVal strS As String) As Boolean
IsSymbol = True
Select Case strS
Case "+"
Case "-"
Case "*"
Case "/"
Case "("
Case ")"
Case "#"
Case Else
IsSymbol = False
End Select
End Function
