#bas
Private Type Parser
   index As Long
   data As String
   oper As Byte
   token As String
End Type
Private Sub Parser_GetToken(ByRef pr As Parser)
    pr.oper = 0
    'Dim c As String
    c = Mid(pr.data, pr.index, 1) ' Вот на эту гадость он ругается, только сменю pr.index на какое-нибудь число, так все сразу ок
    While c = " " And pr.index < Len(pr.data)
      pr.index = pr.index + 1
      c = Mid(pr.data, pr.index, 1)
    Wend
'select block
    If c >= "0" And c <= "9" Then
     pr.oper = 1
     While c >= "0" And c <= "9" And pr.index < Len(pr.data)
         pr.token = pr.token + c
         pr.index = pr.index + 1
         c = Mid(pr.data, pr.index, 1)
     Wend
    Else
      If c = "+" Or c = "-" Or c = "*" Or c = "/" Then
          pr.oper = 2
          pr.token = c
          pr.index = pr.index + 1
      Else
          If c = "(" Or c = ")" Then
              pr.oper = 3
              pr.token = c
              pr.index = pr.index + 1
          Else
            MsgBox "Unknown token at position" + Str$(pr.index)
          End If
      End If
    End If
End Sub
Private Function Parser_Parse(ByRef pr As Parser) As Double
    pr.oper = 0
    pr.index = 0
    Dim x As Double
    Parser_GetToken pr
    Parser_level1 pr, x
    If pr.oper = 0 Then Parser_Parse = 0 Else Parser_Parse = x
End Function
Private Sub Parser_level1(ByRef pr As Parser, ByRef x As Double) '+ -
    Parser_level2 pr, x
    If pr.oper <> 0 Then
        Dim y As Double
        Parser_level2 pr, y
        If pr.oper <> 0 Then
            While pr.oper = 2
                Select Case pr.token$
                    Case "+"
                        x = x + y
                    Case "-"
                        x = x - y
                End Select
            Wend
        End If
    End If
End Sub
Private Sub Parser_level2(ByRef pr As Parser, ByRef x As Double) '* /
    Parser_level3 pr, x
    If pr.oper <> 0 Then
        Dim y As Double
        Parser_level3 pr, y
        If pr.oper <> 0 Then
            While pr.oper = 2
                Select Case pr.token$
                    Case "*"
                        x = x * y
                    Case "/"
                        x = x / y
                End Select
            Wend
        End If
    End If
End Sub
Private Sub Parser_level3(ByRef pr As Parser, ByRef x As Double) '()
    If pr.oper = 1 Then
        x = CInt(pr.token)
    Else
        If pr.oper = 3 Then
            Parser_GetToken pr
            If pr.oper <> 0 Then
                Parser_level1 pr, x
                If pr.oper <> 3 And pr.token$ <> ")" Then
                    pr.oper = 0
                    MsgBox "Excepted ')' at line " + Str$(pr.index)
                End If
            End If
        End If
    End If
End Sub

Private Sub Command1_Click()
    Dim pr As Parser
    pr.data = "2 + 2"
    MsgBox Parser_Parse(pr)
End Sub