#include <iostream>
#include <vector>

using namespace std;

// Recursive function.
bool member_of(int x, vector<int> v)
{
    // Base case.
    if (v.size() == 1) return x == v[0];

    // Either x is equal to the head of the vector, or ...
    if (x == v[0]) return true;

    // ... x is in the rest of the vector (recursive case).
    v.erase(v.begin());
    return member_of(x, v);
}

void test(const int value, const vector<int>& vec)
{
    cout << value << " is";
    bool found = member_of(value, vec);

    if (!found) cout << " not";
    cout << " in the vector." << endl;
}

int main()
{
    vector<int> vec;

    vec.push_back(30);
    vec.push_back(10);
    vec.push_back(50);
    vec.push_back(80);
    vec.push_back(60);
    vec.push_back(12);
    vec.push_back(40);
    vec.push_back(20);
    vec.push_back(70);

    cout << "The vector: ";

    for (int i : vec) cout << i << " ";
    cout << endl << endl;

    test(50, vec);
    test(65, vec);
    test(80, vec);
    test(47, vec);
}