how do i do the calculation with a variable in PHP?

Question

Ok so i have 3 variables

 $real_price = 33.00;
 $real_option = 13.00;
 $option_value['price_prefix'] = "-";
 $real_total = $real_price $option_value['price_prefix'] $real_option;

how come i cant do line 4

I need $real_total to be 20.00

i get Parse error: syntax error, unexpected T_VARIABLE

Why should this work? How can the PHP interpreter know what to do when you put three variables in a row? — Felix Kling, Sep 03 '11 at 12:25
See http://stackoverflow.com/questions/2552052/variable-operators-in-php — str, Sep 03 '11 at 12:29
@Rok Kralj No, it's a good solution that only allows a certain list of operators to be used. — Igor Zinov'yev, Sep 03 '11 at 12:41
@Igor: Refresh page more often. Solution listed there is problematic from the point of relying on unstandard extension & performance hit. — Rok Kralj, Sep 03 '11 at 12:45
@Rok Kralj If you edit your answer (perhaps indent the code, or something), I will be able to remove my downvote. — Igor Zinov'yev, Sep 03 '11 at 12:48
@Rok Kralj What do you mean by "the point of relying on unstandard extension & performance hit"? — str, Sep 03 '11 at 17:59
Doing regular arithmetics, instead of bcmath is much faster. Also bcmath didn't exist in — Rok Kralj, Sep 03 '11 at 18:01

score 2 · Accepted Answer · answered Sep 03 '11 at 12:26

2

 $real_price = 33.00;
 $real_option = 13.00;
 $option_value['price_prefix'] = "-";
 eval('$real_total = $real_price '.$option_value['price_prefix'].' $real_option');

Althrough I don't recommend doing it like that. Do it like this:

 $real_price = 33.00;
 $real_option = 13.00;
 $option_value['price_prefix'] = "-";
switch($option_value['price_prefix']) {
case '+': $real_total=$real_price+$real_option; break;
case '-': $real_total=$real_price-$real_option; break;
case '*': $real_total=$real_price*$real_option; break;
}

answered Sep 03 '11 at 12:26

Rok Kralj

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For a quick answer :) I wanted to present how can OP achieve result his way, but presenting nicer alternative. – Rok Kralj Sep 03 '11 at 12:30
The hero with downvote shall present his reasons for doing so. – Rok Kralj Sep 03 '11 at 12:34
I have removed the downvote because you edited the answer and now it's all better. Edit: Oops, it seems that I can't remove my downvote. Sorry. – Igor Zinov'yev Sep 03 '11 at 12:42

how do i do the calculation with a variable in PHP?

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