// stackcmp.cpp: Stack assignments and comparisons
#include <iostream>
#include <vector>
#include <stack>
using namespace std;

int main() {
 stack <int, vector<int> > S, T, U;
 S.push(10); S.push(20); S.push(30);
 cout << "Pushed onto S: 10 20 30\n";
 T = S;
 cout << "after T = S; we have ";
 cout << (S == T ? "S == T" : "S != T") << endl;
 U.push(10); U.push(21);
 cout << "Pushed onto U: 10 21\n";
 cout << "We now have ";
 cout << (S < U ? "S < U" : "S _= U") << endl;
 return 0;
}