// https://godbolt.org/z/d3ExcWP4a
#include <deque>
#include <iostream>
#include <iterator> // ostream_iterator
#include <algorithm> // copy
using namespace std;
ostream& operator<<=(ostream& os, int val) { return os<<val<<'\n'; }
int main() {
deque d{ 4, 6 }; // Create deque<int> with elements
// Insertion
d.push_front(3); // at the front: efficient
d.insert(d.begin()+2, 5); // in the middle: slow
d.push_back(7); // at the end: efficient
// Access
cout <<= d.front(); // from the front: efficient
cout <<= d[3]; // in the middle: efficient
cout <<= d.back(); // from the end: efficient
// Size
cout <<= d.size(); // read size
d.resize(4); // resize (or extend)
// Iterators
copy(d.begin(), d.end(), ostream_iterator<int>(cout, " "));
cout << '\n'; // Output: 3 4 5 6
// Remove
d.pop_front(); // at the front: efficient
d.erase(d.begin()+1); // in the middle: slow
d.pop_back(); // at the end: efficient
d.clear(); // clear
}