void string_xor_with_key(char * str, int len,  char key) {
    for (int i = 0 ; i < len ; i++) {
        str[i]^=key;
    }
}

int array_sum(int * arr, int len) {
    int sum = 0;
    for (int i = 0 ; i< len; i++) {
        sum += arr[i];
    }
    return sum;
}