18. Set Multiple Bits in 8-bit Register

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

uint8_t set_range(uint8_t reg, uint8_t start, uint8_t end) {
    // construct a bitmask with start --> end set
    // (1 << (end+1)) - 1
    // (1 << start) - 1
    uint8_t mask = (1 << (end+1)) - (1 << start);
    return reg | mask;
}

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