Sum of a list of numbers

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

// This function returns the sum of a list of numbers.
int sum(vector<int> list)
{
    int total = 0; // Start with a total of zero.

    // Go from the beginning to the end of the list.
    for (size_t i = 0; i < list.size(); ++i)
    {
        // Add each number to the sum.
        total += list[i];
    }

    return total;
}

int main()
{
    // Create a list of numbers.
    vector<int> number_list = { 1, 2, 3, 4, 5, 6 };

    // Display the sum of the numbers.
    cout << sum(number_list) << endl;

    return 0;
}