I need help making a simple algorythm to load an expression like 100/5+(10+(2*4))

[Jotaf98]

Hi, I'm working on a scripting language (in VB) and it worked fine until I tried to add expressions (like 100/5+(10+(2*4)) )

Can anyone help me with this? My idea would be to seperate it into "steps", and then execute them backwards, like this:

(1+3)-((4+5)-6)

would become

( + )-(     - )
 1 3   ( + ) 6
        4 5

Does anyone have any idea? Fox, Keda, any of the other gurus around?...

[Sastraxi]

Try finding each bracket pair, then making their expressions into a UDT. This UDT could have something like a priority, with #1 being the most nested bracket. Then you could do BEDMAS in these expressions, using whatever math you already have.

[Zaei]

Liek you said, you will have to separate each expression into steps. If you already support something like "10 + 2 - 3", you should be fine. First, loop through your string. At each open paren, increment a counter, and save it's location in an array. At the first close paren, find the location of the last open paren, pull that part of the string out, and find it's value. Save this value. At the next closed paren, use the saved value as a replacement for it's expression. Repeat.

(1+3)-((4+5)-6);

The loop will look like:
open paren, inc counter
1
+
3
close paren, dec counter, exec expression, 4
-
open paren, inc counter
open paren, inc counter
4
+
6
close paren, dec counter, exec expression, 10
-
6
close paren, dec counter, exec expression, 4
semicolon, finish exec, 4 - 4 = 0

Z.

[jim mcnamara]

FWIW - I posted in C/C++ forum a C interpreter. It has a descending parser. Take a look at how parsers work -- you can implement a simple mathematical processor using one in either VB or C. Or you can just steal the math code part.

http://www.vbforums.com/showthread.p...ht=interpreter

[kedaman]

I did a parser in C++ just a few weeks ago for homework. I bet you don't want to learn C++ now Jotaf so I could instead introduce you to something even more usefull for a vb programmer: Vbscript.
Vbscript can evaluate most string expressions containing both mathematical operators as well as many vb functions. you can look up msdn for more details. That's usefull ofcourse but vbscript is rather more usefull as a scripting language since it's "object oriented" and can work with COM objects you pass to it as well as execute compiled blocks of code at runtime. It might take several months to get a scripting language for similar functionality and with vbscript you have everything just made up for you.

[Jotaf98]

Keda: I already knew about VB-Script, thanks for the tip anyway, but the whole idea was to make a scripting language WITHOUT VB-Script or anything like that

Jim: Thanks, I'll look at your interpreter and maybe I'll get some ideas

Zaei: That was kinda what I was trying to do, but couldn't get some working code to seperate the parts of the expression. Thanks

Sas: I tried UDTs but the code got too complicated and still didn't work, so I decided to start it all over again. Btw, what's "BEDMAS"?

[kedaman]

That's the whole idea? May I ask why?

[Sastraxi]

Americans may know it by PPMDAS -- it's the order of operations.

Brackets
Exponents
Division
Multiplication
Addition
Subtraction

[Jotaf98]

Sas: well, I'm not american ( ) but I see what you mean, it's how you solve equations. Except that my teacher didn't have to give us something like that so we would remember the correct order (she just gave us the list and we learned to use it)

Keda: Why would you hack into the Pentagon if you thought you had the skills for that? I'm doing this because I don't have anything else to do; also to prove myself that I can make a powerful scripting engine run at an acceptable speed in a VB game For the same reasones why we make free programs, games and DLLs sometimes. If you're a programmer, you should already know that

Jim: Thanks for the code, it's a bit too complicated for me (sorry ) but I think it would still be useful if you packed it up in a DLL for use in games

Anyway, I finally managed to code what I wanted. Open up a new VB project, create a textbox and a command button in the form, and dump this code into it:

Option Base 1
Option Explicit
 
Private Sub Command1_Click()
    Dim i As Long, Str As String, TempStr As String
    Dim Stack() As Long, NumStack As Long, Total As Long
    Dim k As Long
    
    Str = Text1.Text
    
    For i = 1 To Len(Str)
        If i > Len(Str) Then Exit For
        
        TempStr = Mid(Str, i, 1)
        
        If TempStr = "(" Then
            NumStack = NumStack + 1
            ReDim Preserve Stack(NumStack)
            
            Stack(NumStack) = i
        ElseIf TempStr = ")" Then
            Total = ExecExpr2(Mid(Str, Stack(NumStack) + 1, i - Stack(NumStack) - 1))
            
            Str = Left(Str, Stack(NumStack) - 1) & Total & Right(Str, Len(Str) - i)
            
            i = Stack(NumStack)
            
            NumStack = NumStack - 1
            If NumStack > 0 Then ReDim Preserve Stack(NumStack)
        End If
    Next i
    
    Total = ExecExpr2(Str, True)
    
    Text1.Text = Total
End Sub
 
Private Function ExecExpr2(Str As String) As Long
    Dim j As Long, TempStr As String
    Dim Total As Long, Stack As String, Op As String * 1
    Dim k As Long
    
    For j = 1 To Len(Str)
        TempStr = Mid(Str, j, 1)
        
        If TempStr = "+" Or TempStr = "-" Or TempStr = "*" Or TempStr = "/" Then
            If Op = Chr(0) Then
                Op = TempStr
                Total = Stack
                Stack = ""
            Else
                If Op = "+" Then
                    Total = Total + Stack
                ElseIf Op = "-" Then
                    Total = Total - Stack
                ElseIf Op = "*" Then
                    Total = Total * Stack
                ElseIf Op = "/" Then
                    Total = Total / Stack
                End If
                
                Stack = ""
                Op = TempStr
            End If
        ElseIf TempStr <> " " Then
            Stack = Stack & TempStr
        End If
    Next j
    
    If Op = "+" Then
        Total = Total + Stack
    ElseIf Op = "-" Then
        Total = Total - Stack
    ElseIf Op = "*" Then
        Total = Total * Stack
    ElseIf Op = "/" Then
        Total = Total / Stack
    End If
    
    ExecExpr2 = Total
End Function

That's it! Type a simple expression into it and press the button; the textbox now has the result.

It's not commented yet, but if you step trough it with F8 it really helps

There's only one problem, it doesn't deal well with negative numbers well (like -10*3 or 200/-4 ). Could you please help me on this one? If you're interested, I can comment the code... basically I followed Zaei's steps, with some suggestions from Sas (except for the UDTs ).
My idea is to load the minus signs differently, so instead of 1 - 2 it would be like 1 + (-2). What do you think?

[Zaei]

For negative numbers, preprocess your string. Find any place with a minus sign. If it is followed and preceded by a number, do nothing. if it followed, but not preceded by a number, insert a 0 before the minus sign, and exec as normal. You may want to add parens around the 0-num, so it works right always.

[Sastraxi]

Listen to Zaei; he's already got a scripting language under his belt =)

[kedaman]

I tell you what Jotaf, If you absolutely don't have anything else to do, and want to test your skills. Learn C++ immediately and you will thank me some day.

[kedaman]

Originally posted by Zaei
For negative numbers, preprocess your string. Find any place with a minus sign. If it is followed and preceded by a number, do nothing. if it followed, but not preceded by a number, insert a 0 before the minus sign, and exec as normal. You may want to add parens around the 0-num, so it works right always.

What are you guys? Amateurs?
(-x) is the unary negate operator, which should not be mistaken for the binary (x-y) substract operator.

[Jotaf98]

Keda: I don't wanna learn C++ because I'm learning Asm
(So I can speed up my VB apps)

Zaei: Thanks! My problem was that the number before the minus sign was nothing (when it was like 10*-4, I'd get the number between the * and the -, which is nothing), so all I have to do is set it to 0

Is anyone here interested in this scripting language, once it's ready? Its syntax is kinda like C++/Java, but it's highly customizable and it's easy to add your own functions

[Jotaf98]

Hum it's giving me different results than the calculator
It's probably because it doesn't make multiplications and divisions before additions and subtractions.

The best method would probably be to put brackets around them, but I'd have to do it BEFORE I start working on the expression - because it's built so it only loops trough the expression ONCE (it's a scripting engine, it must be fast ), so changing the order of the operations in the middle of it wouldn't be very good

So I'll have to make another loop trough it to put brackets in the right places... but this isn't as simple as it seems, can someone please help me? Even the smallest idea would do

[Zaei]

If you want fast, write a compiled psudo-ASM scripting language. The one i am working with(that i wrote), in a few tests performed better then VB =).

Z.

[Zaei]

kedaman, from my tests, 0-x is -x. 0-3 = -3, 0--3 = 3... works for me.

Z.

[kedaman]

Jotaf, do as you wish
Zaei, did your language compile blocks of code like vb script does?

0-x will be a waste of preprocessing time, especially as you have to count in all predecessing situations like a*-b and a^-(b+c) to add extra parentesis.

[Zaei]

It compiles the entire script into bytecode. The only real downside is that it's psudo asm:

mov aa 10
add aa 10
shl aa 1
push aa
int 0
call hello
end

function hello
mov aa 10
push aa
int 10
ret

And that you can only use variable names aa..zz, but that was a speed consideration =).

Z.

[Jotaf98]

Zaei: How do you think my scripting language works? Except that it converts the blocks into asm-like code (but it's not REAL asm, just "jump here", "set var to this", etc)

And I'm gonna assign an index to each var so it'll be even faster

Kedaman: It's not a waste of preprocessing time, actually all I had to do was If TempStr="" Then TempStr="0"