задача от семинар

#include<iostream>

bool isMemberOf(const int* arr, const int arg, const int& length, int currIndex = 0) {
    if (arr[0] == arg)
        return true;

    if (currIndex >= length)
        return false;

    return isMemberOf(arr + 1, arg, length, currIndex + 1);
}

bool isAllEven(const int* arr, const int& len, int currNumber = 0) {
    if (currNumber == len)
        return true;

    if (isMemberOf(arr, 2 * currNumber, len))
        return true && isAllEven(arr, len, currNumber + 1);

    return false;
}

int main() {
    int arr[5] = { 0, 2, 4, 6, 9 };
    std::cout << isAllEven(arr, 5);
    arr[4] = 8;
    std::cout << isAllEven(arr, 5);
}