PHP calculator increase - php

Question

I am creating simple calculator. I am just learning php and this is a small project.I have created a calculator with two inputs but I am now testing it with just one. It works but only if you type number+number. It doesn't work if it is number+number+number.
I would like that it would work if you inputted 2+2+2... or 2*2*2... or 6-2-2... and 2/2/2...
Code:
// Create Variables
$y = $_POST["input1"];
// Echo input value on screen
echo "<p>Operation: " . $y . "</p>";
// Validation
if(empty($y)){
?>
<script>
$(document).ready(function(){
$('#error').append('Error: Your Input is empty');
});
</script>
<?php
}elseif(preg_match("/[a-zA-Z]/", $y)){
?>
<script>
$(document).ready(function(){
$('#error').append('Error: You can only input numbers');
});
</script>
<?php
}else{
// Calculation Brain FOR + Operator
if (strpos($y,'+') !== false) {
$omega = substr($y, 0, strpos($y, '+'));
$alpha = substr($y, strpos($y, '+') + 1);
echo "<p>Omega: " . $omega . "</p>";
echo "<p>Alpha: " . $alpha . "</p>";
$gamma = $omega + $alpha;
// The Sum FOR + operator
echo "Calculation: " . $gamma;
}
}

Answer 1

That's usually a bad practice, but here you can use eval. But you have first to check that your string doesn't contains disallowed characters.
$allowedCharacters = "0123456789./*-+()% ";
if(preg_match('/^[^'.preg_quote($allowedCharacters).']+$/'), $y) {
eval('$result = '.$y.';');
echo "Calculation: " . $result;
}
The only problem is that you'll not be able to handle errors.

Answer 2

you could use this for the same operation
$test='2+2*3';
eval('$calc = '.$test.';');
echo "Calculation: " . $calc;
the out should be : 8