这个抽象算法早已为人所知，只不过在VB的公开文档中鲜见示例代码。于是，为了提高自己的程序设计水平，锻炼自己的能力，我写了如下代码。
【VB代码版权所有，允许转载修改用作学习目的，转载必须注明来源】
【求大家看完后留言啊！】
堆栈类的实现：
1 Private Stack() As String 2 Private itemCount As Long 3 Private Sub Class_Initialize() 4 ReDim Stack(0) 5 Stack(0) = "#" 6 End Sub 7 Public Sub Push(ByVal inString As String) 8 ReDim Preserve Stack(itemCount + 1) 9 Stack(itemCount + 1) = inString 10 itemCount = itemCount + 1 11 End Sub 12 13 Public Function Pop() As String 14 If itemCount >= 1 Then 15 Pop = Stack(itemCount) 16 ReDim Preserve Stack(itemCount - 1) 17 itemCount = itemCount - 1 18 Else 19 Pop = "" 20 End If 21 End Function 22 Public Function Peek() As String 23 If itemCount = 0 Then 24 Peek = "" 25 Exit Function 26 End If 27 Peek = Stack(itemCount) 28 End Function 29 30 Sub Clear() 31 itemCount = 0 32 ReDim Stack(itemCount) 33 Stack(itemCount) = "#" 34 End Sub 35 36 Public Function Count() 37 Count = itemCount 38 End Function 39 Public Function ViewStack() As String 40 Dim kOut As String 41 Dim i As Long 42 If itemCount = 0 Then ViewStack = "": Exit Function 43 For i = 1 To itemCount 44 kOut = kOut & Format(i, "00") & " " & Stack(i) & vbCrLf 45 Next i 46 ViewStack = kOut 47 End Function
计算模块中的代码：
1 Public opNum As New StackClass 2 Public opChar As New StackClass 3 Public Function CalcString(ByVal strIn As String) As String 4 Dim sTxt As String 5 Dim strNumFix As String 6 Dim curChar As String 7 Dim i As Long 8 Dim signCount As Long 9 Dim ops1 As String, ops2 As String, opC As String 10 '初始化堆栈 11 opNum.Clear 12 opChar.Clear 13 '堆栈初始化结束 14 sTxt = strIn 15 For i = 1 To Len(sTxt) 16 curChar = Mid(sTxt, i, 1) 17 If IsSymbol(curChar) = True Then 18 '看看数字预备区有没有 19 If strNumFix <> "" Then 20 opNum.Push strNumFix 21 strNumFix = "" 22 End If 23 redo: 24 If IsHigh(curChar, opChar.Peek) = 1 Then 'if new come char is higher then push it to stack 25 opChar.Push curChar '如果等级高的控制符，则进入 26 signCount = signCount + 1 27 ElseIf IsHigh(curChar, opChar.Peek) = 0 Then 28 If curChar = "#" And opChar.Peek = "#" Then 29 opChar.Pop 30 CalcString = opNum.Pop 31 Exit Function 32 End If 33 ElseIf IsHigh(curChar, opChar.Peek) = -1 Then 'if low then ready to calculate 34 '判断是不是第一个符号 35 If signCount = 1 Then '这个符号是刚刚输入#后的那个，无论如何入栈 36 opChar.Push curChar 37 signCount = signCount + 1 38 GoTo nextone 39 End If 40 ops2 = opNum.Pop 41 ops1 = opNum.Pop 42 opC = opChar.Pop 43 opNum.Push CStr(Calc(ops1, ops2, opC)) 44 If curChar = ")" And opChar.Peek = "(" Then 45 opChar.Pop '如果操作数是），就把（弹出来 46 GoTo moveon 47 End If 48 GoTo redo 49 moveon: 50 End If 51 Else '非符号 52 strNumFix = strNumFix & curChar 53 End If 54 nextone: 55 Next i 56 End Function 57 58 Public Function Calc(ByVal op1 As String, ByVal op2 As String, ByVal options As String) As Double 59 On Error Resume Next 60 Calc = 0 61 Select Case options 62 Case "+" 63 Calc = CDbl(op1) + CDbl(op2) 64 Case "-" 65 Calc = CDbl(op1) - CDbl(op2) 66 Case "*" 67 Calc = CDbl(op1) * CDbl(op2) 68 Case "/" 69 Calc = CDbl(op1) / CDbl(op2) 70 End Select 71 End Function 72 73 Public Function IsHigh(ByVal sNew As String, ByVal sOld As String) As Integer 74 '1大于，-1小于，0等于 75 Select Case sNew 76 Case "+" 77 Select Case sOld 78 Case "(" 79 IsHigh = 1 80 Exit Function 81 Case "#" 82 IsHigh = 1 83 Exit Function 84 Case Else 85 IsHigh = -1 86 Exit Function 87 End Select 88 Case "-" 89 Select Case sOld 90 Case "(" 91 IsHigh = 1 92 Exit Function 93 Case "#" 94 IsHigh = 1 95 Exit Function 96 Case Else 97 IsHigh = -1 98 Exit Function 99 End Select 100 Case "*" 101 Select Case sOld 102 Case "(" 103 IsHigh = 1 104 Exit Function 105 Case "#" 106 IsHigh = 1 107 Exit Function 108 Case "+" 109 IsHigh = 1 110 Exit Function 111 Case "-" 112 IsHigh = 1 113 Exit Function 114 Case Else 115 IsHigh = -1 116 Exit Function 117 End Select 118 Case "/" 119 Select Case sOld 120 Case "(" 121 IsHigh = 1 122 Exit Function 123 Case "#" 124 IsHigh = 1 125 Exit Function 126 Case "+" 127 IsHigh = 1 128 Exit Function 129 Case "-" 130 IsHigh = 1 131 Exit Function 132 Case Else 133 IsHigh = -1 134 Exit Function 135 End Select 136 Case "(" 137 Select Case sOld 138 Case "+" 139 IsHigh = 1 140 Exit Function 141 Case "-" 142 IsHigh = 1 143 Exit Function 144 Case "*" 145 IsHigh = 1 146 Exit Function 147 Case "/" 148 IsHigh = 1 149 Exit Function 150 Case "(" 151 IsHigh = 1 152 Exit Function 153 Case Else 154 IsHigh = -1 155 Exit Function 156 End Select 157 Case ")" 158 IsHigh = -1 159 Exit Function 160 Case "" 161 IsHigh = -1 162 Exit Function 163 Case "#" 164 Select Case sOld 165 Case "#" 166 IsHigh = 0 167 Exit Function 168 Case "" 169 IsHigh = 1 170 Exit Function 171 Case "+" 172 IsHigh = -1 173 Exit Function 174 Case "-" 175 IsHigh = -1 176 Exit Function 177 Case "*" 178 IsHigh = -1 179 Exit Function 180 Case "/" 181 IsHigh = -1 182 Exit Function 183 Case ")" 184 IsHigh = -1 185 Exit Function 186 End Select 187 End Select 188 End Function 189 190 Public Function IsSymbol(ByVal strS As String) As Boolean 191 IsSymbol = True 192 Select Case strS 193 Case "+" 194 Case "-" 195 Case "*" 196 Case "/" 197 Case "(" 198 Case ")" 199 Case "#" 200 Case Else 201 IsSymbol = False 202 End Select 203 End Function
