Replace Bit Field in a 32-bit Register

#include <stdio.h>
#include <stdint.h>
#define CHECK_BIT(reg, pos) ((reg) & (1 << pos))
#define SET_BIT(reg, pos) ((reg) |= (1 << pos))
#define CLEAR_BIT(reg, pos) ((reg) &= ~(1 << pos))

uint32_t replace_field(uint32_t reg, uint32_t val, uint8_t pos, uint8_t len) {
    // Your code here
    for (int i = pos; i < pos + len; i++) {
        if (CHECK_BIT(val, i-pos)) {
            SET_BIT(reg, i);
        }
        else {
            CLEAR_BIT(reg, i);
        }
    }
    return reg;
}

int main() {
    uint32_t reg, val;
    uint8_t pos, len;
    scanf("%u %u %hhu %hhu", &reg, &val, &pos, &len);
    printf("%u", replace_field(reg, val, pos, len));
    return 0;
}