Returning an iterator using non-member begin() and end() function

Prior to modern C++, to iterate a sequence, we call the begin() and end() member method of each container. For array, we can iterate its element by iterating the index. Since C++11, the language has a non-member function--begin() and end()--to retrieve the iterator of the sequence. Let's suppose we have an array of the following elements:

    int arr[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

When the language doesn't have the begin() and end() function, we need to iterate the elements of the array using the index we can see in the following lines of code:

    for (unsigned int i = 0; i < sizeof(arr)/sizeof(arr[0]); ++i)
    // Do something to the array

Fortunately, using the begin() and end() function, we can refactor the preceding for loop to become as follows:

    for (auto i = std::begin(arr); i != std::end(arr); ++i)
    // Do something to the array

As we can see, the use of the begin() and end() function creates a compact code since we don't need to worry about the length of the array because the iterator pointer of begin() and end() will do it for us. For comparison, let's take a look at the following begin_end.cpp code:

    /* begin_end.cpp */
    #include <iostream>

    auto main() -> int
    {
      std::cout << "[begin_end.cpp]" << std::endl;

      // Declaring an array
      int arr[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

      // Displaying the array elements
      // using conventional for-loop
      std::cout << "Displaying array element using conventional for-
       loop";
      std::cout << std::endl;
      for (unsigned int i = 0; i < sizeof(arr)/sizeof(arr[0]); ++i)
      std::cout << arr[i] << " ";
      std::cout << std::endl;

      // Displaying the array elements
      // using non-member begin() and end()
      std::cout << "Displaying array element using non-member begin()
       and end()";
      std::cout << std::endl;
      for (auto i = std::begin(arr); i != std::end(arr); ++i)
       std::cout << *i << " ";
      std::cout << std::endl;

      return 0;
    }

To prove the preceding code, we can compile the code, and, when we run it, the following output should be displayed on the console screen:

As we can see in the screenshot, we've got the exact same output when we use the conventional for-loop or begin() and end() functions.