calculate math expression from a string using eval

Question

I want to calculate math expression from a string. I have read that the solution to this is to use eval(). But when I try to run the following code:

<?php  $ma ="2+10"; $p = eval($ma); print $p;  ?> 

It gives me the following error:

Parse error: syntax error, unexpected $end in C:\xampp\htdocs\eclipseWorkspaceWebDev\MandatoryHandinSite\tester.php(4) : eval()'d code on line 1

Does someone know the solution to this problem.

Answer 1

While I don't suggest using eval for this (it is not the solution), the problem is that eval expects complete lines of code, not just fragments.

$ma ="2+10"; $p = eval('return '.$ma.';'); print $p; 

Should do what you want.

---

A better solution would be to write a tokenizer/parser for your math expression. Here's a very simple regex-based one to give you an example:

$ma = "2+10";  if(preg_match('/(\d+)(?:\s*)([\+\-\*\/])(?:\s*)(\d+)/', $ma, $matches) !== FALSE){     $operator = $matches[2];      switch($operator){         case '+':             $p = $matches[1] + $matches[3];             break;         case '-':             $p = $matches[1] - $matches[3];             break;         case '*':             $p = $matches[1] * $matches[3];             break;         case '/':             $p = $matches[1] / $matches[3];             break;     }      echo $p; } 

Answer 2

Take a look at this..

I use this in an accounting system where you can write math expressions in amount input fields..

Examples

$Cal = new Field_calculate();  $result = $Cal->calculate('5+7'); // 12 $result = $Cal->calculate('(5+9)*5'); // 70 $result = $Cal->calculate('(10.2+0.5*(2-0.4))*2+(2.1*4)'); // 30.4 

Code

class Field_calculate {     const PATTERN = '/(?:\-?\d+(?:\.?\d+)?[\+\-\*\/])+\-?\d+(?:\.?\d+)?/';      const PARENTHESIS_DEPTH = 10;      public function calculate($input){         if(strpos($input, '+') != null || strpos($input, '-') != null || strpos($input, '/') != null || strpos($input, '*') != null){             //  Remove white spaces and invalid math chars             $input = str_replace(',', '.', $input);             $input = preg_replace('[^0-9\.\+\-\*\/\(\)]', '', $input);              //  Calculate each of the parenthesis from the top             $i = 0;             while(strpos($input, '(') || strpos($input, ')')){                 $input = preg_replace_callback('/\(([^\(\)]+)\)/', 'self::callback', $input);                  $i++;                 if($i > self::PARENTHESIS_DEPTH){                     break;                 }             }              //  Calculate the result             if(preg_match(self::PATTERN, $input, $match)){                 return $this->compute($match[0]);             }             // To handle the special case of expressions surrounded by global parenthesis like "(1+1)"             if(is_numeric($input)){                 return $input;             }              return 0;         }          return $input;     }      private function compute($input){         $compute = create_function('', 'return '.$input.';');          return 0 + $compute();     }      private function callback($input){         if(is_numeric($input[1])){             return $input[1];         }         elseif(preg_match(self::PATTERN, $input[1], $match)){             return $this->compute($match[0]);         }          return 0;     } }