问在C中转换基数时出现有趣的printf()错误

EN

char* getBase(unsigned int a, int base) {
    char buffer[33];

    char digits[] = "0123456789ABCDEF";

    if(base < 2 || base > 16) {
        printf("Invalid base");
        return NULL;
    }

    char* cn = &buffer[sizeof(buffer) - 1];
    *cn = '\0';

    do {
        cn -= 1;
        *cn = digits[a % base];
        a /= base;
    } while(a > 0);

    printf("\n"); //HERE

    return cn;
}

int main() {
    printf("%s", getBase(8, 2));
    return 0;
}