22. Extract Even Bits Only from 32-bit Register

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

uint32_t extract_even_bits(uint32_t reg) {
    // Your code here
    uint32_t mask, result;
    mask=1;
    result=0;
    while (mask != 0) {
        result |= (mask & reg);
        mask = mask << 1;
        reg = reg >> 1;
    }
    return result;
}

int main() {
    uint32_t reg;
    scanf("%u", &reg);
    printf("%u", extract_even_bits(reg));
    return 0;
}

Use a rolling mask of 1, AND it with reg and put in result.

Then right shift the reg and left shift the mask, till the 1 runs out the end of mask.