List back () function in C++ STL

The list::back () function of the C++ STL returns a direct reference to the last element in the list container. This function varies from list::end (), which just returns an iterator to the last entry.

Syntax:

list_name. back ()

Parameters

This function doesn't accept any parameters.

Return Value: This function directly references the last element in the list container example list. Although this function does not contain such an exception, applying it on a list container that is empty results in an undefined behaviour in C++.

Errors and Exception

1. When the list container is empty, it shows unknown behaviour results.
2. It ensures that no exceptions will be thrown, if the list is not empty.

// C++ program of list back() function 
#include <iostream>
#include <list>
usingnamespacestd;
 
intmain()
{
    list<int>mylist{ 1, 2, 3, 4, 5 };
    cout<<mylist.back();
    return0;
}

Output:

The list::back() function is illustrated in the program below.

// assign() method for lists
#include <bits/stdc++.h>
usingnamespacestd;
 
intmain()
{
    // list creation from scratch
    list<int>demo_list;
 
    // Including more items to the list
    demo_list.push_back(10);
    demo_list.push_back(20);
    demo_list.push_back(30);
 
    // prints the last element of demo_list
    cout<<demo_list.back();
 
    return0;
}

Output:

Time Complexity: O(1)

Auxiliary Space: O(1)

Application

Print the difference between the first and last entry after adding numbers to an empty list of integers.

Input: 1,2,3,4,5,6,7,8

Output: 7

Explanation: final component =8, initial component=1, difference=7

Algorithm

1. Using the push front() or push back() function, add numbers to the list.
2. Compare the first and last components.
3. Subtract the last element from the first element if it is larger, then print the result.
4. Otherwise, divide the first element by the last element and output the result.

Code:

// CPP programme to exemplify
// application of the functions front() and back()
#include <iostream>
#include <list>
usingnamespacestd;
 
intmain()
{
    list<int>mylist{};
    mylist.push_front(8);
    mylist.push_front(7);
    mylist.push_front(6);
    mylist.push_front(5);
    mylist.push_front(4);
    mylist.push_front(3);
    mylist.push_front(2);
    mylist.push_front(1);
 
    // listing is now 1, 2, 3, 4, 5, 6, 7, and 8.
 
    if(mylist.front() >mylist.back()) {
        cout<<mylist.front() - mylist.back();
    }
    elseif(mylist.front() <mylist.back()) {
        cout<<mylist.back() - mylist.front();
    }
    else
        cout<< "0";
}

Output: