18. Set Multiple Bits in 8-bit Register

#include <stdio.h>
#include <stdint.h>

int powe(int x){
    int res=1;
    while (x>0){
        res*=2;
        x--;
    }
    return res;
}

uint8_t set_range(uint8_t reg, uint8_t start, uint8_t end) {
    return reg | ((powe(end-start+1)-1)<<start) ;
}

int main() {
    uint8_t reg, start, end;
    scanf("%hhu %hhu %hhu", &reg, &start, &end);
    printf("%u", set_range(reg, start, end));
    return 0;
}