C_PRG_LANG_EX_2.6

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>

// in x: n bits start with position p are equals n right bits from y
int setbits(int x, int p, int n, int y)
{
    unsigned int temp = ~(0);
    temp <<= n;

    for(int i = 0; i < p - n + 1; i++)
    {
        temp <<= 1;
        temp |= 1;
    }

    return (x & temp) | (((~((~0) << n)) & y) << (p - n + 1));
}

int main(void)
{
    int p, n, x, y;
    x = 2679;
    y = 1473;
    p = 4;
    n = 3;

    printf("setbits p = %i, n = %i\n", p, n);
    printf("%i\n%i\n%i\n", x, y, setbits(x, p, n, y));

    return 0;
}