Write a function setbits(x, p, n ,y) that returns x with the n bits that begin at position p set to the rightmost n bits of y, leaving the other bits unchanged.

/*setbits: set n bits of x at position p with bits of y   */
unsigned setbits(unsigned x, int p, int n, unsigned y){
   return x & (~(~(~0 << n)  << (p + 1 - n)) | (y & ~(~0 << n)) <<(p +1 - n);
}