c++ String question

#include <iostream>
#include <array>
#include <string>

using namespace std;

int main()
{
  // stl array string.
  array<char,7> stl_array_string {"He\0llo"};

  int null_count {0};

  for ( const auto& a_char : stl_array_string )
  {
    if ( a_char == '\0' )
      ++null_count;
  }
  cout << "null chars iterated over in strange stl array string: " << null_count << endl;
  // cout << "Streams as \"" << stl_array_string << "\"." << endl;
  // Doesn't compile, but given that that's not what it's for, I'm not surprised.


  // c-style array string
  char c_style_array_string[] {"He\0llo"};
  null_count = 0;
  for ( const auto& a_char : c_style_array_string )
  {
    if ( a_char == '\0' )
      ++null_count;
  }
  cout << "null chars iterated over in c-style, array based string: " << null_count << endl;
  cout << "Streams as \"" << c_style_array_string << "\"." << endl;


  // standard string
  string standard_string {"He\0llo"};
  null_count = 0;
  for ( const auto& a_char : standard_string  )
  {
    if ( a_char == '\0' )
      ++null_count;
  }
  cout << "null chars iterated over in standard string: " << null_count << endl;
  cout << "Streams as \"" << standard_string << "\"." << endl;

  return 0;

  // Output is:
  //null chars iterated over in strange stl array string: 2
  //null chars iterated over in c-style, array based string: 2
  //Streams as "He".
  //null chars iterated over in standard string: 0
  //Streams as "He".

}