このコードは基本的に数式を取り、それを評価します。次のコードは、VB.net で恥知らずにここから取得したものです:式の評価
これはJavaで書かれています。
Public Function evaluate(expression As [String]) As Integer
Dim tokens As Char() = expression.ToCharArray()
' Stack for numbers: 'values'
Dim values As New Stack(Of UInteger)()
' Stack for Operators: 'ops'
Dim ops As New Stack(Of Char)()
For i As Integer = 0 To tokens.Length - 1
' Current token is a whitespace, skip it
If tokens(i) = " "c Then
Continue For
End If
' Current token is a number, push it to stack for numbers
If tokens(i) >= "0"c AndAlso tokens(i) <= "9"c Then
Dim sbuf As New StringBuilder(100)
'Dim sbuf As New String("", 128)
' There may be more than one digits in number
If i < tokens.Length AndAlso tokens(i) >= "0"c AndAlso tokens(i) <= "9"c Then
sbuf.Append(tokens(System.Math.Max(System.Threading.Interlocked.Increment(i), i - 1)))
End If
If sbuf Is Nothing AndAlso sbuf.ToString().Equals("") Then
Else
Dim intgr As Integer
Dim accpt As Boolean = Integer.TryParse(sbuf.ToString(), intgr)
If accpt = True Then
values.Push([Integer].Parse(sbuf.ToString()))
Else
Dim space As String = " "
values.Push(space)
End If
End If
' Current token is an opening brace, push it to 'ops'
ElseIf tokens(i) = "("c Then
ops.Push(tokens(i))
' Closing brace encountered, solve entire brace
ElseIf tokens(i) = ")"c Then
While ops.Peek() <> "("c
values.Push(applyOp(ops.Pop(), values.Pop(), values.Pop()))
End While
ops.Pop()
' Current token is an operator.
ElseIf tokens(i) = "+"c OrElse tokens(i) = "-"c OrElse tokens(i) = "*"c OrElse tokens(i) = "/"c Then
' While top of 'ops' has same or greater precedence to current
' token, which is an operator. Apply operator on top of 'ops'
' to top two elements in values stack
While Not ops.Count = 0 AndAlso hasPrecedence(tokens(i), ops.Peek())
values.Push(applyOp(ops.Pop(), values.Pop(), values.Pop()))
End While
' Push current token to 'ops'.
ops.Push(tokens(i))
End If
Next
' Entire expression has been parsed at this point, apply remaining
' ops to remaining values
While Not ops.Count = 0
values.Push(applyOp(ops.Pop(), values.Pop(), values.Pop()))
End While
' Top of 'values' contains result, return it
Return values.Pop()
End Function
Public Function hasPrecedence(op1 As Char, op2 As Char) As [Boolean]
If op2 = "("c OrElse op2 = ")"c Then
Return False
End If
If (op1 = "*"c OrElse op1 = "/"c) AndAlso (op2 = "+"c OrElse op2 = "-"c) Then
Return False
Else
Return True
End If
End Function
' A utility method to apply an operator 'op' on operands 'a'
' and 'b'. Return the result.
Public Function applyOp(op As Char, b As Integer, a As Integer) As Integer
Select Case op
Case "+"c
Return a + b
Case "-"c
Return a - b
Case "*"c
Return a * b
Case "/"c
If b = 0 Then
'Throw New UnsupportedOperationException("Cannot divide by zero")
End If
Return a \ b
End Select
Return 0
End Function
これはコードを使用する方法です:
formula = "10 + 2 * 6"
Dim result As Double = evaluate(formula)
そして、私はこの次のエラーが発生し続けます:
Unhandled exception at line 885, column 13 in http: **** DEDOM5KzzVKtsL1tWZwgsquruscgqkpS5bZnMu2kotJDD8R38OukKT4TyG0z97U1A8ZC8o0wLOdVNYqHqQLlZ9egcY6AKpKRjQWMa4aBQG1Hz8t_HRmdQ39BUIKoCWPik5bv4Ej6LauiiQptjuzBMLowwYrLGpq6dAhVvZcB-4b-mV24vCqXJ3jbeKi0&t=6119e399
0x800a139e - Microsoft JScript ランタイム エラー: Sys.WebForms.PageRequestManagerServerErrorException: 文字列 " " から型 'UInteger' への変換が無効です。
私は初心者ですが、スペースを整数に変換できないためにエラーが発生していると思います.スペースを処理するには?? どんな助けでも大歓迎です:)。