230问答网 > 急求VB程序设计一个简单的四则表达式计算程序急急急急急！！！！！！！！

急求VB程序设计一个简单的四则表达式计算程序急急急急急！！！！！！！！

2025-02-13 05:25:33

推荐回答（4个）

回答1：

以前整的，可能对你有用，看看吧
VERSION 5.00
Begin VB.Form ExpressionForm
Caption = "Expression"
ClientHeight = 2310
ClientLeft = 1380
ClientTop = 2100
ClientWidth = 6615
LinkTopic = "Form1"
PaletteMode = 1 'UseZOrder
ScaleHeight = 2310
ScaleWidth = 6615
Begin VB.TextBox ExprText
Height = 285
Left = 0
TabIndex = 0
Top = 360
Width = 3615
End
Begin VB.CommandButton CmdEvaluate
Appearance = 0 'Flat
BackColor = &H80000005&
Caption = "Evaluate"
Default = -1 'True
Height = 495
Left = 1200
TabIndex = 11
Top = 960
Width = 1215
End
Begin VB.Frame Frame1
Appearance = 0 'Flat
Caption = "Primitives"
ForeColor = &H80000008&
Height = 2295
Left = 3720
TabIndex = 12
Top = 0
Width = 2895
Begin VB.TextBox NameText
Height = 285
Index = 0
Left = 240
TabIndex = 1
Top = 480
Width = 1215
End
Begin VB.TextBox ValueText
Height = 285
Index = 0
Left = 1560
TabIndex = 2
Top = 480
Width = 1215
End
Begin VB.TextBox NameText
Height = 285
Index = 1
Left = 240
TabIndex = 3
Top = 840
Width = 1215
End
Begin VB.TextBox ValueText
Height = 285
Index = 1
Left = 1560
TabIndex = 4
Top = 840
Width = 1215
End
Begin VB.TextBox NameText
Height = 285
Index = 2
Left = 240
TabIndex = 5
Top = 1200
Width = 1215
End
Begin VB.TextBox ValueText
Height = 285
Index = 2
Left = 1560
TabIndex = 6
Top = 1200
Width = 1215
End
Begin VB.TextBox NameText
Height = 285
Index = 3
Left = 240
TabIndex = 7
Top = 1560
Width = 1215
End
Begin VB.TextBox ValueText
Height = 285
Index = 3
Left = 1560
TabIndex = 8
Top = 1560
Width = 1215
End
Begin VB.TextBox NameText
Height = 285
Index = 4
Left = 240
TabIndex = 9
Top = 1920
Width = 1215
End
Begin VB.TextBox ValueText
Height = 285
Index = 4
Left = 1560
TabIndex = 10
Top = 1920
Width = 1215
End
Begin VB.Label Label1
Appearance = 0 'Flat
Caption = "Name"
ForeColor = &H80000008&
Height = 255
Index = 0
Left = 240
TabIndex = 14
Top = 240
Width = 615
End
Begin VB.Label Label1
Appearance = 0 'Flat
Caption = "Value"
ForeColor = &H80000008&
Height = 255
Index = 1
Left = 1560
TabIndex = 13
Top = 240
Width = 615
End
End
Begin VB.Label Label2
Appearance = 0 'Flat
Caption = "Expression"
ForeColor = &H80000008&
Height = 255
Left = 0
TabIndex = 17
Top = 0
Width = 975
End
Begin VB.Label Label3
Appearance = 0 'Flat
Caption = "Result"
ForeColor = &H80000008&
Height = 255
Left = 480
TabIndex = 16
Top = 1800
Width = 615
End
Begin VB.Label ResultLabel
BorderStyle = 1 'Fixed Single
Height = 255
Left = 1200
TabIndex = 15
Top = 1800
Width = 1215
End
End
Attribute VB_Name = "ExpressionForm"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Option Explicit

Dim Primitives As Collection

' ************************************************
' Evaluate the expression.
' ************************************************
Private Function EvaluateExpr(ByVal expr As String) As Single
Const PREC_NONE = 11
Const PREC_UNARY = 10 ' Not actually used.
Const PREC_POWER = 9
Const PREC_TIMES = 8
Const PREC_DIV = 7
Const PREC_INT_DIV = 6
Const PREC_MOD = 5
Const PREC_PLUS = 4

Dim is_unary As Boolean
Dim next_unary As Boolean
Dim parens As Integer
Dim pos As Integer
Dim expr_len As Integer
Dim ch As String
Dim lexpr As String
Dim rexpr As String
Dim value As String
Dim status As Long
Dim best_pos As Integer
Dim best_prec As Integer

' Remove leading and trailing blanks.
expr = Trim$(expr)
expr_len = Len(expr)
If expr_len = 0 Then Exit Function

' If we find + or - now, it is a unary operator.
is_unary = True

' So far we have nothing.
best_prec = PREC_NONE

' Find the operator with the lowest precedence.
' Look for places where there are no open
' parentheses.
For pos = 1 To expr_len
' Examine the next character.
ch = Mid$(expr, pos, 1)

' Assume we will not find an operator. In
' that case the next operator will not
' be unary.
next_unary = False

If ch = " " Then
' Just skip spaces.
next_unary = is_unary
ElseIf ch = "(" Then
' Increase the open parentheses count.
parens = parens + 1

' An operator after "(" is unary.
next_unary = True
ElseIf ch = ")" Then
' Decrease the open parentheses count.
parens = parens - 1

' An operator after ")" is unary.
next_unary = True

' If parens < 0, too many ')'s.
If parens < 0 Then
Err.Raise vbObjectError + 1001, _
"EvaluateExpr", _
"Too many )s in '" & _
expr & "'"
End If
ElseIf parens = 0 Then
' See if this is an operator.
If ch = "^" Or ch = "*" Or _
ch = "/" Or ch = "\" Or _
ch = "%" Or ch = "+" Or _
ch = "-" _
Then
' An operator after an operator
' is unary.
next_unary = True

Select Case ch
Case "^"
If best_prec >= PREC_POWER Then
best_prec = PREC_POWER
best_pos = pos
End If

Case "*", "/"
If best_prec >= PREC_TIMES Then
best_prec = PREC_TIMES
best_pos = pos
End If

Case "\"
If best_prec >= PREC_INT_DIV Then
best_prec = PREC_INT_DIV
best_pos = pos
End If

Case "%"
If best_prec >= PREC_MOD Then
best_prec = PREC_MOD
best_pos = pos
End If

Case "+", "-"
' Ignore unary operators
' for now.
If (Not is_unary) And _
best_prec >= PREC_PLUS _
Then
best_prec = PREC_PLUS
best_pos = pos
End If
End Select
End If
End If
is_unary = next_unary
Next pos

' If the parentheses count is not zero,
' there's a ')' missing.
If parens <> 0 Then
Err.Raise vbObjectError + 1002, _
"EvaluateExpr", "Missing ) in '" & _
expr & "'"
End If

' Hopefully we have the operator.
If best_prec < PREC_NONE Then
lexpr = Left$(expr, best_pos - 1)
rexpr = Right$(expr, expr_len - best_pos)
Select Case Mid$(expr, best_pos, 1)
Case "^"
EvaluateExpr = _
EvaluateExpr(lexpr) ^ _
EvaluateExpr(rexpr)
Case "*"
EvaluateExpr = _
EvaluateExpr(lexpr) * _
EvaluateExpr(rexpr)
Case "/"
EvaluateExpr = _
EvaluateExpr(lexpr) / _
EvaluateExpr(rexpr)
Case "\"
EvaluateExpr = _
EvaluateExpr(lexpr) \ _
EvaluateExpr(rexpr)
Case "%"
EvaluateExpr = _
EvaluateExpr(lexpr) Mod _
EvaluateExpr(rexpr)
Case "+"
EvaluateExpr = _
EvaluateExpr(lexpr) + _
EvaluateExpr(rexpr)
Case "-"
EvaluateExpr = _
EvaluateExpr(lexpr) - _
EvaluateExpr(rexpr)
End Select
Exit Function
End If

' If we do not yet have an operator, there
' are several possibilities:
'
' 1. expr is (expr2) for some expr2.
' 2. expr is -expr2 or +expr2 for some expr2.
' 3. expr is Fun(expr2) for a function Fun.
' 4. expr is a primitive.
' 5. It's a literal like "3.14159".

' Look for (expr2).
If Left$(expr, 1) = "(" And Right$(expr, 1) = ")" Then
' Remove the parentheses.
EvaluateExpr = EvaluateExpr(Mid$(expr, 2, expr_len - 2))
Exit Function
End If

' Look for -expr2.
If Left$(expr, 1) = "-" Then
EvaluateExpr = -EvaluateExpr( _
Right$(expr, expr_len - 1))
Exit Function
End If

' Look for +expr2.
If Left$(expr, 1) = "+" Then
EvaluateExpr = EvaluateExpr( _
Right$(expr, expr_len - 1))
Exit Function
End If

' Look for Fun(expr2).
If expr_len > 5 And Right$(expr, 1) = ")" Then
lexpr = LCase$(Left$(expr, 4))
rexpr = Mid$(expr, 5, expr_len - 5)
Select Case lexpr
Case "sin("
EvaluateExpr = Sin(EvaluateExpr(rexpr))
Exit Function
Case "cos("
EvaluateExpr = Cos(EvaluateExpr(rexpr))
Exit Function
Case "tan("
EvaluateExpr = Tan(EvaluateExpr(rexpr))
Exit Function
Case "sqr("
EvaluateExpr = Sqr(EvaluateExpr(rexpr))
Exit Function
End Select
End If

' See if it's a primitive.
On Error Resume Next
value = Primitives.Item(expr)
status = Err.Number
On Error GoTo 0
If status = 0 Then
EvaluateExpr = CSng(value)
Exit Function
End If

' It must be a literal like "2.71828".
On Error Resume Next
EvaluateExpr = CSng(expr)
status = Err.Number
On Error GoTo 0
If status <> 0 Then
Err.Raise status, _
"EvaluateExpr", _
"Error evaluating '" & expr & _
"' as a constant."
End If
End Function

' ************************************************
' Evaluate the expression entered by the user.
' ************************************************
Private Sub CmdEvaluate_Click()
Dim i As Integer
Dim name As String
Dim value As String
Dim expr As String
Dim rslt As Single
Dim pos As Integer

' Store the primitives.
Set Primitives = New Collection
For i = 0 To 4
name = Trim$(NameText(i).Text)
value = Trim$(ValueText(i).Text)
If name <> "" And value <> "" Then
Primitives.Add value, name
End If
Next i

' Get the expression.
expr = ExprText.Text

' Evaluate the expression.
ResultLabel.Caption = ""
On Error GoTo EvaluateError
rslt = EvaluateExpr(expr)
ResultLabel.Caption = Format$(rslt)
Exit Sub

EvaluateError:
Beep
MsgBox Err.Description
End Sub