deque::end results in assertion failure

I was coding some code which needs a deque of structs. Only after 300 lines of repeatedly debugged code and excessive over-engineering, I found out that using the deque::end function somehow doesn't work in this code.

Below is a simplified version of the code:

vvv code vvv

#include <iostream>
#include <deque>
#define lli signed long long int
using namespace std;
typedef struct cityData
{
	lli height;
	lli index;
} cityData;
int main()
{
	deque<cityData> city;
	lli cityCount;
	cin >> cityCount;
	for (lli i = 1; i <= cityCount; i++)
	{
		cityData input;
		cin >> input.height;
		input.index = i;
		city.push_back(input);
	}
	cout << "firstIndex: " << city.begin()->index << endl;
	cout << "lastIndex: " << city.end()->index << endl;
}

vvv Input vvv

10
9 2 8 3 7 2 8 2 9 1

vvv Output vvv

firstIndex: 1
error: cannot dereference out of range deque iterator
code terminated with exit code 3.

any idea on how to solve the issue?

I wanted to create a code which contains a deque of structs, however, an error occured when I used the function deque::end on the program.

deque::end() returns an iterator to an element past the last element, and it mustn't be dereferenced.

You can use deque::back() to refer to the last element. (This returns a reference to an element, not an iterator)