How to extract substring by start-index and end-index?

Question

$str = \'HelloWorld\';
$sub = substr($str, 3, 5);
echo $sub; // prints \"loWor\"

I know that substr() takes the first parameter, 2nd parameter is start

Answer 1

It's just math

$sub = substr($str, 3, 5 - 3);

The length is the end minus the start.