Issue

This question has a short answer. Using the eval() method causes php to fully resolve the formula and return the correct result.

$expression = "27+38+81+48*33*53+91*53+82*14+96";
$result = eval('return '.$expression.';');
$ Echo the result.
 

How can I solve this problem without using eval()?

Solution

The functions below will parse simple mathematical expressions and calculate the result.

<?php
    
    echo "90165: ".calculate("27+38+81+48*33*53+91*53+82*14+96")."\n";

    // calculates the result of an expression in infix notation
    function calculate($exp) {
        return calculate_rpn(mathexp_to_rpn($exp));
    }

    // calculates the result of an expression in reverse polish notation
    function calculate_rpn($rpnexp) {
        $stack = array();
        foreach($rpnexp as $item) {
            if (is_operator($item)) {
                if ($item == '+') {
                    $j = array_pop($stack);
                    $i = array_pop($stack);
                    array_push($stack, $i + $j);
                }
                if ($item == '-') {
                    $j = array_pop($stack);
                    $i = array_pop($stack);
                    array_push($stack, $i - $j);
                }
                if ($item == '*') {
                    $j = array_pop($stack);
                    $i = array_pop($stack);
                    array_push($stack, $i * $j);
                }
                if ($item == '/') {
                    $j = array_pop($stack);
                    $i = array_pop($stack);
                    array_push($stack, $i / $j);
                }
                if ($item == '%') {
                    $j = array_pop($stack);
                    $i = array_pop($stack);
                    array_push($stack, $i % $j);
                }
            } else {
                array_push($stack, $item);
            }
        }
        return $stack[0];
    }

    // converts infix notation to reverse polish notation
    function mathexp_to_rpn($mathexp) {
        $precedence = array(
            '(' => 0,
            '-' => 3,
            '+' => 3,
            '*' => 6,
            '/' => 6,
            '%' => 6
        );
    
        $i = 0;
        $final_stack = array();
        $operator_stack = array();

        while ($i < strlen($mathexp)) {
            $char = $mathexp{$i};
            if (is_number($char)) {
                $num = readnumber($mathexp, $i);
                array_push($final_stack, $num);
                $i += strlen($num); continue;
            }
            if (is_operator($char)) {
                $top = end($operator_stack);
                if ($top && $precedence[$char] <= $precedence[$top]) {
                    $oper = array_pop($operator_stack);
                    array_push($final_stack, $oper);
                }
                array_push($operator_stack, $char);
                $i++; continue;
            }
            if ($char == '(') {
                array_push($operator_stack, $char);
                $i++; continue;
            }
            if ($char == ')') {
                // transfer operators to final stack
                do {
                    $operator = array_pop($operator_stack);
                    if ($operator == '(') break;
                    array_push($final_stack, $operator);
                } while ($operator);
                $i++; continue;
            }
            $i++;
        }
        while ($oper = array_pop($operator_stack)) {
            array_push($final_stack, $oper);
        }
        return $final_stack;
    }

    function readnumber($string, $i) {
        $number = '';
        while (is_number($string{$i})) {
            $number .= $string{$i};
            $i++;
        }
        return $number;
    }

    function is_operator($char) {
        static $operators = array('+', '-', '/', '*', '%');
        return in_array($char, $operators);
    }

    function is_number($char) {
        return (($char == '.') || ($char >= '0' && $char <= '9'));
    }
?>

The function mathexp_to_rpn() converts a mathematical expression in infix notation, like "3 + 2" to an expression in reverse polish notation (RPN): "3 2 +". This is easier to calculate, which is done by the function calculate_rpn(). Operator precedence and parenthesis is taken into account. There is no checking whether the input is a valid expression. Dividing is not very precise.

Source

Answered By – noah1400

Answer Checked By – Candace Johnson (Easybugfix Volunteer)

Tags: php