std::deque<T,Allocator>::back
Min standard notice:
Returns a reference to the last element in the container.
# Declarations
reference back();
const_reference back() const;
# Return value
Reference to the last element.
# Notes
For a non-empty container c, the expression c.back() is equivalent to *std::prev(c.end()).
# Example
#include <cassert>
#include <deque>
int main()
{
std::deque<char> letters{'a', 'b', 'c', 'd'};
assert(letters.back() == 'd');
}