Detailed code explanation of the calculation formula in string format through eval in PHP

Sometimes we have a commission formula for each product, and this formula for calculating commission is stored in the table in the format of string . When we use this calculation formula, it does not As we wrote: $a=2+3*5;, the result can be calculated simply, and it is a string, so we must convert the string into a result that we can process

There are At that time, we had a commission formula for each product, and the formula for calculating the commission was stored in the table in string format. When we used this calculation formula, it did not look like what we wrote: $a=2+3 *5; This is a simple way to calculate the result, and it is a string. Therefore, we must convert the string into a result that we can process
And the eval() function in php can Processing php code, so you can use this to solve: calculation formula stored in string format

For example:

$str='2*(3+12)';
$result=eval("return $str;");
echo $result;

will output: 30

It is the value of expression

The return $str; in eval() is the php code

Of course, the value of variable can also be brought in :

$a=3;
$b=12;
$str='2*($a+$b)';
$result=eval("return $str;");
echo $result;

will output: 30

This way, the code to implement the calculator in PHP is implemented, mainly using the eval function of PHP.

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