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) 
{
    uint8_t mask = 0;
    uint8_t number_of_bits = end - start + 1;
    for (int i = 0; i < number_of_bits; i++) {
        mask |= (1 << i);
    }
    reg |= (mask << start);
    return reg;

}

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