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Value of string expression

Posted on 1999-06-22
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Last Modified: 2010-05-02
Dear Sir,

we want the value of string expression. i.e. if i pass "5*5-2" in string then it will return 23 in integer. So how can i do this ? Please give me solution of this problem because it is very important for us.

TIA

With regards,

Nilesh shah
Aurokripa Softwares
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Question by:Aurokripa
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4 Comments
 
LVL 18

Accepted Solution

by:
deighton earned 400 total points
ID: 1518871
VERSION 4.00
Begin VB.Form Form1
   Caption         =   "Form1"
   ClientHeight    =   5880
   ClientLeft      =   1140
   ClientTop       =   1545
   ClientWidth     =   6690
   Height          =   6300
   Left            =   1080
   LinkTopic       =   "Form1"
   ScaleHeight     =   5880
   ScaleWidth      =   6690
   Top             =   1185
   Width           =   6810
   Begin VB.TextBox Text1
      Height          =   1335
      Left            =   2040
      TabIndex        =   1
      Text            =   "Text1"
      Top             =   3840
      Width           =   2655
   End
   Begin VB.CommandButton Command1
      Caption         =   "Command1"
      Height          =   1215
      Left            =   2160
      TabIndex        =   0
      Top             =   1560
      Width           =   1455
   End
End
Attribute VB_Name = "Form1"
Attribute VB_Creatable = False
Attribute VB_Exposed = False
Dim e_input As String     ' Expression input string.
Dim e_tok As String       ' Current token kind.
Dim e_spelling As String  ' Current token spelling.
Dim e_error As Integer    ' Tells if syntax error occurred.

Function e_eval(ByVal s As String, value As Double) As Integer
   ' Initialize.
   e_error = 0
   e_input = s
   Call e_nxt
 
   ' Evaluate.
   value = e_prs(1)
 
   ' Check for unrecognized input.
   If e_tok <> "" And Not e_error Then
      MsgBox "syntax error, token = '" + e_spelling + "'"
   e_error = -1
   End If
 
   e_eval = Not e_error
End Function
 
' e_prs
'   Parse an expression, allowing operators of a specified
'   precedence or higher. The lowest precedence is 1.
'   This function gets tokens with e_nxt and recursively
'   applies operator precedence rules.
Function e_prs(p As Integer) As Double
   Dim n As Double    ' Return value.
   Dim fun As String  ' Function name.
 
   ' Parse expression that begins with a token (precedence 12).
   If e_tok = "num" Then
      ' number.
      n = Val(e_spelling)
      Call e_nxt
   ElseIf e_tok = "-" Then
      ' unary minus.
      Call e_nxt
      n = -e_prs(11)    ' Operand precedence 11.
   ElseIf e_tok = "not" Then
      ' logical NOT.
      Call e_nxt
      n = Not e_prs(6)  ' Operand precedence 6.
   ElseIf e_tok = "(" Then
      ' parentheses.
      Call e_nxt
      n = e_prs(1)
      Call e_match(")")
   ElseIf e_tok = "id" Then
      ' Function call.
      fun = e_spelling
      Call e_nxt
      Call e_match("(")
      n = e_prs(1)
      Call e_match(")")
      n = e_function(fun, n)
   Else
      If Not e_error Then
         MsgBox "syntax error, token = '" + e_spelling + "'"
         e_error = -1
      End If
   End If
 
   ' Parse binary operators.
Do While Not e_error
  If 0 Then  ' To allow ElseIf .
  ElseIf p <= 11 And e_tok = "^" Then: Call e_nxt: n = n ^ e_prs(12)
  ElseIf p <= 10 And e_tok = "*" Then: Call e_nxt: n = n * e_prs(11)
  ElseIf p <= 10 And e_tok = "/" Then: Call e_nxt: n = n / e_prs(11)
  ElseIf p <= 9 And e_tok = "\" Then: Call e_nxt: n = n \ e_prs(10)
  ElseIf p <= 8 And e_tok = "mod" Then: Call e_nxt: n = n Mod e_prs(9)
  ElseIf p <= 7 And e_tok = "+" Then: Call e_nxt: n = n + e_prs(8)
  ElseIf p <= 7 And e_tok = "-" Then: Call e_nxt: n = n - e_prs(8)
  ElseIf p <= 6 And e_tok = "=" Then: Call e_nxt: n = n = e_prs(7)
  ElseIf p <= 6 And e_tok = "<" Then: Call e_nxt: n = n < e_prs(7)
  ElseIf p <= 6 And e_tok = ">" Then: Call e_nxt: n = n > e_prs(7)
  ElseIf p <= 6 And e_tok = "<>" Then: Call e_nxt: n = n <> e_prs(7)
  ElseIf p <= 6 And e_tok = "<=" Then: Call e_nxt: n = n <= e_prs(7)
  ElseIf p <= 6 And e_tok = ">=" Then: Call e_nxt: n = n >= e_prs(7)
  ElseIf p <= 5 And e_tok = "and" Then: Call e_nxt: n = n And e_prs(6)
  ElseIf p <= 4 And e_tok = "or" Then: Call e_nxt: n = n Or e_prs(5)
  ElseIf p <= 3 And e_tok = "xor" Then: Call e_nxt: n = n Xor e_prs(4)
  ElseIf p <= 2 And e_tok = "eqv" Then: Call e_nxt: n = n Eqv e_prs(3)
  ElseIf p <= 1 And e_tok = "imp" Then: Call e_nxt: n = n Imp e_prs(2)
  Else
       Exit Do
  End If
 Loop
 
   e_prs = n
End Function
 
' e_function.
'   Evaluate a function. This is a helper function to simplify
'   e_prs.
Function e_function(fun As String, arg As Double) As Double
   Dim n As Double
 
   Select Case LCase$(fun)
   Case "abs": n = Abs(arg)
   Case "atn": n = Atn(arg)
   Case "cos": n = Cos(arg)
   Case "exp": n = Exp(arg)
   Case "fix": n = Fix(arg)
   Case "int": n = Int(arg)
   Case "log": n = Log(arg)
   Case "rnd": n = Rnd(arg)
   Case "sgn": n = Sgn(arg)
   Case "sin": n = Sin(arg)
   Case "sqr": n = Sqr(arg)
   Case "tan": n = Tan(arg)
   Case Else
      If Not e_error Then
         MsgBox "undefined function '" + fun + "'"
         e_error = -1
      End If
   End Select
 
   e_function = n
End Function
 
' e_nxt
'   Get the next token into e_tok and e_spelling and remove the
'   token from e_input.
'   This function groups the input into "words" like numbers,
'   operators and function names.
Sub e_nxt()
   Dim is_keyword As Integer
   Dim c As String  ' Current input character.
 
   e_tok = ""
   e_spelling = ""
 
   ' Skip whitespace.
   Do
      c = Left$(e_input, 1)
      e_input = Mid$(e_input, 2)
   Loop While c = " " Or c = Chr$(9) Or c = Chr$(13) Or c = Chr$(10)
 
   Select Case LCase$(c)
 
   ' Number constant. Modify this to support hexadecimal, etc.
   Case "0" To "9", "."
      e_tok = "num"
      Do
         e_spelling = e_spelling + c
         c = Left$(e_input, 1)
         e_input = Mid$(e_input, 2)
      Loop While (c >= "0" And c <= "9") Or c = "."
      e_input = c + e_input
 
   ' Identifier or keyword.
   Case "a" To "z", "_"
      e_tok = "id"
      Do
         e_spelling = e_spelling + c
         c = LCase$(Left$(e_input, 1))
         e_input = Mid$(e_input, 2)
         is_id% = (c >= "a" And c <= "z")
         is_id% = is_id% Or c = "_" Or (c >= "0" And c <= "9")
      Loop While is_id%
      e_input = c + e_input
 
      ' Check for keyword.
      is_keyword = -1
      Select Case LCase$(e_spelling)
         Case "and"
         Case "eqv"
         Case "imp"
         Case "mod"
         Case "not"
         Case "or"
         Case "xor"
         Case Else: is_keyword = 0
      End Select
      If is_keyword Then
         e_tok = LCase$(e_spelling)
      End If
 
   ' Check for <=, >=, <>.
   Case "<", ">"
      e_tok = c
      c = Left$(e_input, 1)
      If c = "=" Or c = ">" Then
         e_tok = e_tok + c
         e_input = Mid$(e_input, 2)
      End If
 
   ' Single character token.
   Case Else
      e_tok = c
   End Select
 
    If e_spelling = "" Then
       e_spelling = e_tok
   End If
End Sub
 
' e_match
'   Check the current token and skip past it.
'   This function helps with syntax checking.
Sub e_match(token As String)
   If Not e_error And e_tok <> token Then
      MsgBox "expected " + token + ", got '" + e_spelling + "'"
      e_error = -1
   End If
   Call e_nxt
End Sub
Private Sub Command1_Click()
   
       Dim n As Double
 
       If e_eval(Text1.Text, n) Then
         MsgBox Format$(n)
       End If
   
End Sub



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LVL 18

Expert Comment

by:deighton
ID: 1518872
If you want to use integers only with divide you can use the integer divide \ operator with my program.
0
 

Expert Comment

by:mholywell
ID: 1518873
The easiest way is to use the script control to figure this out for you :

1) add the component microsoft script control
2)place the new control on your form (it will be named
  scriptcontrol1 by default)
3)Text1 = "5*5-2"
  intX=scriptcontrol1.eval(text1)

and intx will be 23!
0
 

Author Comment

by:Aurokripa
ID: 1518874
We are very thankful to you.  Thanks for providing excellent solution. We hope for the best help in future like does at present.  
0

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