$re = '/^((?:\d[+*]){0,49}\d)$/m';
$str = '1+2*3*8+0
9
9*9
the 99 character expression
1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+5*8
And these would not be valid:
1++1
12+1
2*25
1+
47
+
+1
11
100+ character length
1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+5*8+9';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php