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) 
{
    if(start < end)
    {
    int8_t mask = ((1 << (end-start+1))-1)<<start;
    reg |= mask;
    return reg;       
    }
    else if(start>end)
    {
        printf("start bit position must be less than end bit position");
    }
    else{
        printf("invalid start and end bits");
    }
    return 0;
}

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