ptt freshman mid-exam question 2

q2.c

void q2(int n) {
    bool shown = false;
    char one_zero;
    int n2 = 0x80;

 CAL:
    if (n >= n2) {
        n -= n2;
        one_zero = '1';
    } else {
        one_zero = '0';
    }

    if (shown) {
        putchar('_');
        putchar(one_zero);
    } else {
        if (one_zero == '1' || n2 == 1) {
            shown = true;
            putchar(one_zero);
        }
    }

    if (n2 > 1) {
        n2 /= 2;
        goto CAL;
    } else {
        putchar('\n');
    }
}