cppreference.com > C++ Vectors > back back Syntax:
      #include <vector>
      TYPE& back();
      const TYPE& back() const;
The back() function returns a reference to the last element in the vector. For example:
     vector<int> v;
     for( int i = 0; i < 5; i++ ) {
       v.push_back(i);
     }
     cout << "The first element is " << v.front()
          << " and the last element is " << v.back() << endl;
This code produces the following output:
     The first element is 0 and the last element is 4
The back() function runs in constant time. Related topics: front pop_back