PHP Help with function and for combined

Question

I got this question in a test, with the advice o clues I got an answer of 10 but I did not get it, somebody can help me step by step?

What output results from the following code?
function func($arg) {
$result = 0;
for($i=0; $i<$arg; $i++) {
$result = $result + $i;
}
return $result;
}
echo func(5);

Answer 1

It's adding the numbers from 0 to $arg-1. In this case $arg == 5.

1+2+3+4 == 10.