why the output of the following program is 147?

Question

$x=1;
while ($x<10){
echo $x;
$x=$x+3;
}
please explain a little bit.

Answer 1

x >=1 and less than 10
and your algorithm adds 3 to each value of x
thus: when x ->1
x~1+3 ->4
when x=4
x~4+3 ->7
...so x=147