theory - Tail v. Head Recursion -

i wondering if identify head or tail recursive function:

int exponentiation(int x, int y){     if(!y) { return 1; }     return y > 1 ? x * exponentiation(x, y-1) : x; } 

this not tail recursion: returning result of exponentiation not last action taken function; multiplication x is.

however, function easy convert tail-recursive implementation adding parameter, exp:

int exponentiation_tail(int x, int y, int exp = 1){     if(y <= 0) { return exp; }     return exponentiation_tail(x, y-1, exp*x); }