- is_numeric: documentation ( source)
- mb_substr: documentation ( source)
- mb_strlen: documentation ( source)
<?php
$input = '20-5*2/30+9=';
$inputLength = mb_strlen($input);
$number = 0;
$result = 0;
$op = '';
for ($i = 0; $i < $inputLength; $i++) {
$char = mb_substr($input, $i, 1);
if ($char == '*' || $char == '+' || $char == '-' || $char == '=' || $char == '/') {
if ($op == '') {
$result = $number;
} elseif ($op == '+') {
$result += $number;
} elseif ($op == '-') {
$result -= $number;
} elseif ($op == '*') {
$result *= $number;
} elseif ($op == '/') {
$result /= $number;
}
echo "op[$op] result[$result] number[$number] char[$char] \n";
$op = $char;
$number = 0;
if ($char == '=') {
echo "Ответ: $input$result";
}
} elseif (is_numeric($char) || $char == '.') {
$number = $number * 10 + intval($char);
} else {
echo "Неверный символ:'$char\n";
exit();
}
}