Объявляем функции:
| Код |
Private Function EvaluateExpr(ByVal expr As String) As Single
On Error Resume Next
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 not unary.
next_unary = False
' 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$(expr, best_pos, 1)
Case "^"
'If lexpr <> 0 Then
EvaluateExpr = _
EvaluateExpr(lexpr) ^ _
EvaluateExpr(rexpr)
'Else
' EvaluateExpr = 0
'End If
Case "*"
EvaluateExpr = _
EvaluateExpr(lexpr) * _
EvaluateExpr(rexpr)
Case "/"
EvaluateExpr = _
EvaluateExpr(lexpr) / _
EvaluateExpr(rexpr)
Case "\"
EvaluateExpr = _
EvaluateExpr(lexpr) \ _
EvaluateExpr(rexpr)
Case "%"
EvaluateExpr = _
EvaluateExpr(lexpr) Mod _
EvaluateExpr(rexpr)
Case "+"
EvaluateExpr = _
EvaluateExpr(lexpr) + _
EvaluateExpr(rexpr)
Case "-"
EvaluateExpr = _
EvaluateExpr(lexpr) - _
EvaluateExpr(rexpr)
End Select
Exit Function
End If
' If we do not yet have an operator, there
' are several possibilities:
'
' 1. expr is (expr2) for some expr2.
' 2. expr is -expr2 or +expr2 for some expr2.
' 3. expr is Fun(expr2) for a function Fun.
' 4. expr is a primitive.
' 5. It's a literal like "3.14159".
' Look for (expr2).
If Left$(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 "atn("
EvaluateExpr = Atn(EvaluateExpr(rexpr))
Exit Function
Case "sqr("
EvaluateExpr = Sqr(EvaluateExpr(rexpr))
Exit Function
Case "log("
EvaluateExpr = Log(EvaluateExpr(rexpr)) / Log(10)
Exit Function
Case "lne("
EvaluateExpr = Log(EvaluateExpr(rexpr))
Exit Function
Case "exp("
EvaluateExpr = Exp(EvaluateExpr(rexpr))
Exit Function
Case "abs("
EvaluateExpr = Abs(EvaluateExpr(rexpr))
Exit Function
End Select
End If
On Error Resume Next
EvaluateExpr = CSng("0" & 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
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Выводим сообщение:
| Код |
MsgBox EvaluateExpr("1 + (2 *4)")
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И ещё. Если пример подоёдёт, нен нада затруднять себя сообщениями об этом. Просто повысь репутацию.
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