【原创】VB利用堆栈实现算术表达式计算

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。

【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

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原文地址：https://www.cnblogs.com/sunsoftresearch/p/3037271.html