Evaluate a Text Formula

dcox94

Hello,

I have users create a formula which is saved in a database field. I am having a hard time evaluating this formula.

for example I am saving the string:
"$my_profit * 0.4"

$formula ="$my_profit * 0.4"; // as retrieved from the database
$my_profit = 1000;

echo $formula;  // this returns: $my_profit * 0.4

eval("\$formula=\"$formula\";");
echo $formula;  // this returns: 1000 * 0.4

How do I get 400 (the result of 1000 * 0.4) ?

Thanks,
Dan

dgrinberg

Hi,

Just use single quotes! It gets too messy when you are trying to escape everything.

The following works just fine.

<?php

$formula ='$my_profit * 0.4'; 
$my_profit = 1000;

echo $formula.'<br>';  // this returns: $my_profit * 0.4

eval('$formula = '.$formula.';');
echo $formula.'<br>';  // this returns: 400

?>

Using the single quotes means that PHP will not try to evaluate the variables inside the string before you want it to.

dcox94

I got it after a little more reading on eval().

Changed the formula to:
"$my_results = $my_profit * 0.4;"

$formula ="$my_results = $my_profit * 0.4;";  // as retrieved from the database
$my_profit = 1000;

echo $formula;  // this returns: $my_results = $my_profit * 0.4;

eval($formula);

echo $my_results;  // this returns: 400

Thanks

Originally posted by dcox94
Hello,

I have users create a formula which is saved in a database field. I am having a hard time evaluating this formula.

for example I am saving the string:
"$my_profit * 0.4"
$formula ="$my_profit * 0.4"; // as retrieved from the database
$my_profit = 1000;

echo $formula;  // this returns: $my_profit * 0.4

eval("\$formula=\"$formula\";");
echo $formula;  // this returns: 1000 * 0.4
How do I get 400 (the result of 1000 * 0.4) ?

Thanks,
Dan

dcox94

dgrinberg,

That is easier and it works great!

Thanks!
Dan

Originally posted by dgrinberg
Hi,

Just use single quotes! It gets too messy when you are trying to escape everything.

The following works just fine.
<?php

$formula ='$my_profit * 0.4'; 
$my_profit = 1000;

echo $formula.'<br>';  // this returns: $my_profit * 0.4

eval('$formula = '.$formula.';');
echo $formula.'<br>';  // this returns: 400

?>
Using the single quotes means that PHP will not try to evaluate the variables inside the string before you want it to. [/B]