NetNews Usenet Archive 1992 #26/NN_1992_26.iso/spool/comp/lang/pascal/6545

Text File | 1992-11-12 | 2.5 KB | 69 lines

Newsgroups: comp.lang.pascal
Path: sparky!uunet!ukma!darwin.sura.net!udel!sbcs.sunysb.edu!csws2.ic.sunysb.edu!clane
From: [e-mail] (Charles F Lane)
Subject: Re: Help Converting : ='x+y' to :=x+y
Message-ID: <[e-mail]>
Sender: [e-mail] (Usenet poster)
Nntp-Posting-Host: csws2.ic.sunysb.edu
Organization: State University of New York at Stony Brook
References: <[e-mail]>
Date: Fri, 13 Nov 1992 00:38:52 GMT
Lines: 56

In article <[e-mail]> [e-mail] (Paul Smedshammer) writes:
>I don't know if this is a simple thing to do but I have not
>been able to figure it out.  I would like to take a string
>of characters that represent an equation and implement that
>equation.  For example:
>
>     Var  Equation : String[20];
>          x, y, Solution : Real;
>     Begin
>          Equation := 'x + y';
>          x := 1;
>          y := 2;
>             {'now right here I would like to be able
>             to use the equation in the string Equation
>             like this:
>          Solution := Somefunction(Equation);
>             Is this easily done?'}
>          Writeln('The solution is:',Equation,'=',Solution);
>     End.

Just use a case statement after detecting the operator (+,-,*,/)
in the string:

  var Operator : char;  {Add this to your other vars}

  for i := 1 to ord(Equation[0]) do
   if Equation[i] in ['+','-','*','/']
   then Operator := Equation[i]
   else Operator := 'Z';

  case Operator of
   '+' : Solution := x+y;
   '-' : Solution := x-y;
   '*' : Solution := x*y;
   '/' : Solution := x/y;
   else {print some error message that there's no operator in the string};
  end;

You may want to make your operator detection algorithm a bit more robust
than the above, but I kept it simple for unerstandability.  I'm a bit
confused about your assignments to x and y.  You'll need to detect the two
numbers in the string, as well -- unless the numbers are already known and
all you want the user to do is indicate an equation to operate on the numbers.

[stuff deleted]
>------------------------------------------------------------------------------
>[e-mail] (Paul Smedshammer)
>
>Graduate Student in Mechanical Engineering
>California State University at Chico
>------------------------------------------------------------------------------

--
                          | "So who is this Al Gorithm guy they keep
Charles F. Lane           |  mentioning in my Computer Science classes?"
[e-mail]|