<?php
error_reporting(-1);
$input = "243+6743-78*2=";
$inputLength = mb_strlen($input);

$number = 0;
$result = 0;
$op = '';

for ($i = 0; $i < $inputLength; $i++) {
	
	$char = mb_substr($input, $i, 1);
	
	if($char == '*' || $char == '+' || $char == '-' || $char == '=') {
		switch($op) {
			case '':
				$result += $number;
				$number = 0;
				break;
			case '+':
				$result += $number;
				$number = 0;
				break;	
			case '-':
				$result -= $number;
				$number = 0;
				break;
			case '*':
				$result *= $number;
				$number = 0;
				break;
			case '/':
				$result /= $number;
				$number = 0;
				break;
		}
		$op = $char;
		
		if($op == '=') {
			echo $input . $result;
		}
		
	} elseif(is_numeric($char)) {
		$number = $number * 10 + intval($char);
	} else {
		echo "Wrong sign: '$char'\n";
	}
	
}