How to Safely Evaluate Mathematical Expressions from Strings in PHP?

Evaluating Mathematical Expressions from Strings Using Eval

Issue:

When attempting to evaluate a mathematical expression stored in a string using eval(), a "Parse error" occurs, indicating an unexpected end of input.

Solution:

While it's generally not recommended to use eval() for this purpose due to security concerns, the following code modification resolves the issue:

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

By explicitly returning the result within an eval() function, the code expects a complete line of code.

Alternative Solution:

A more secure and efficient solution is to use a tokenizer/parser to handle mathematical expressions. Here's a simple regex-based 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;
}

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