Difference between clear() and erase() methods of a vector in c++?

Question

Following is the main function of my program, I could not find any difference between clear() and erase() of vector, then why in following code I am getting diferent results when I use erase() instead of clear()?

 int main()
 {
    int notest, N, temp;
    long long sum, profit;
    int count;

    vector<int> S;
    S.reserve(50009);
    cin>>notest;

    for(int test=0; test<notest; test++)
   {
       profit = 0;
       cin>>N;
    for(int i=0; i<N; i++)
    {
            cin>>temp;
            S.push_back(temp);

    }

    DO SOME THING HERE
    S.clear();      
}


 }

Here clear() is not producing the desired results, but when I use erase I get desired results, why?

Solution 1

clear() removes all elements from the vector leaving behind a vector of size zero while erase() deletes a single element or a range of elements from the vector.

Solution 2

Erase takes a parameter - the thing to erase. clear dumps the lot.

As per the manual http://en.cppreference.com/w/cpp/container/vector