6. std::stack

• A stack is a container that permits to insert and extract its elements only from the top of the container:

  
      #include <cassert>
      #include <stack>
  
      using namespace std;
  
      int main (int argc, char* argv[])
      {
          stack< int > st;
  
          st.push( 100 );           // push number on the stack
          assert( st.size() == 1 ); // verify one element is on the stack
          assert( st.top() == 100 );// verify element value
  
          st.top() = 456;           // assign new value
          assert( st.top() == 456 );
  
          st.pop();                 // remove element
          assert( st.empty() == true );
          
          return 0;
      }