Question about php

Question

Function math($t) {
If ($t == 0)
return 0;
return $t + math($t - 1);
}
echo math(6);

Can somebody explain me how i get result 21 here, i'm new to php and i try to understand this.

function expo($b, $e) {
if ($e == 0)
return 1;
$result = $b;
for ($i = 1; $i < $e; $i++)
$result;
}
echo expo(2,3);

Also in this one, result is 8 and i don't understand why is 8.
Thank you in advance.

Answer 1

On first iteration the function math(6) has 6 as argument and this maths function will execute till 0 as at argument 0 it is return 0.
Now look over that
1) return 6+ math(6-1)
2) return 6+5+math(5-1)
3) return 6+5+4+ math(4-1)
4) return 6+5+4+3+math(3-1)
5) return 6+5+4+3+2+math(2-1)
6) return 6+5+4+3+2+1+ math(1-1)
7) return 6+5+4+3+2+1+0
As math(0) return 0 now sum all return value
6+5+4+3+2+1+0=21
So output is 21

Answer 2

Now I understand it, thank you so much man!! Preity