Clear Specific Bits in a 32-bit Register

#include <stdio.h>
#include <stdint.h>
// 1U <<  = 10000 -1 = 01111 = 1000
uint32_t clear_bits(uint32_t reg, uint8_t pos, uint8_t len) {
    // Your code here
    uint32_t pre=0;
    for(int i =0; i<=len-1;i++){
        pre = pre | (1U<<i);
    }
    pre = ~(pre << pos);
    reg = reg & pre;
    return reg ;
}

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