Average of grades

#include <iostream>
#include <vector>
using namespace std;

// Enter any number of grades.
// Display the average.
int main()
{
    vector<int> list_of_grades;
    float sum_of_grades = 0;
    float grade_average = 0;
    float grade = 0; // Each grade entered by user.


    cout << "Enter grades one by one, enter '-1' when done.\n";
    cin >> grade;
    while (grade != -1) // Until user is done,
    {
        list_of_grades.push_back(grade); // Add grade to list.
        cout << "Grade: "; // Ask for next grade.
        cin >> grade; // Get grade.
    }

    if (list_of_grades.size() > 0) // If at least one grade is entered,
    {
        for (int item : list_of_grades) // For each grade on the list,
        {
            sum_of_grades += item; // Add the grade to the sum.
        }

        // Calculate the average.
        grade_average = sum_of_grades / list_of_grades.size();

        // Display the average.
        cout << "The average grade is: " << grade_average << '\n';
    }
    else // Otherwise, if no grades were entered,
    {
        cout << "No grades were entered.\n";
    }


    // End the program.
    return 0;
}