Given two integers x and n, write a function to compute xn. We may assume that x and n are small and overflow doesn’t happen.
Input : x = 2, n = 3
Output : 8
Input : x = 7, n = 2
Output : 49
Calculate power (x,y) using recursion : https://www.geeksforgeeks.org/write-a-c-program-to-calculate-powxn/