Evaluating a String

[trndyrock]

I am developing a dynamic graphing application with php, and the GD Library. It is dynamic in the sense that a user inputs an equation into a text box, and the equation is sent to a .php page where the equation is evaluated and then a graph is produced. I have everything I need to a point. Once the form is submitted, the equation is sent as a string and not as a mathematical equation. So, for example, the user inputs x+2, I have a loop that will go back and replace any x's with a variable x, and the variable x is set and changed, to 10 different numbers, 0 to 10, so that I can get a y-coordinate. But I can never get the $x+2 to evaluate. my expected result would be:

0,2
1,3
and so on.
But instead, I get:
0, 0+2
1, 1+2

Any ideas?

[tsinka]

Hi,

I tried this code and it worked on my server (it supports more complex functions also as long as you define all base variable correctly:

<?PHP
$x=0;
$z=2;
$y=0;
$arr = array();
$equation = "(x+2)*z";
if (strlen($equation)) {
  $func = $equation;
  $func = preg_replace("/([a-z])/",'\\\\\\$\\\\1',$func);

  for ($x=0;$x<=10;$x++) {
    eval("\$arr['$x'] = $func;");
  }

  foreach($arr as $key => $value) {
    echo "$key,$value<br>\n";
  }
}
?>

The important part is the code inside the if. In order to get this to work with a posted variable replace the if condition and the $func=$equation; line with $_POST code.

Thomas

[trndyrock]

YAY!!

No more headaches! Thanks a bunch!