<?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 == '-' || $char == '=') {
	     echo "op=[$op], result = [$result], number = [$number], char = [$char]\n";
		intval($number);
		if ($op == '') {
			$result = $number;
			$number = 0;
			$op = $char;
		}
		if ($op == '+') {
			$result += $number;
			$number = 0;
			$op = $char;
		}
		if ($op == '-') {
			$result -= $number;
			$number = 0;
			$op = $char;
		}
		if ($op == '*') {
			$result *= $number;
			$number = 0;
			$op = $char;
		}
		if ($char == '=') {
			echo $input . $result;
		}
		
	} elseif (is_numeric($char)) {
        $number = $number * 10 + $char;
	}else {
		echo 'Неверный символ: {$char}\n';
	}
}