manipulations with elements of vector and structure C++

Question

For understanding more difficult processes and operations with vectors, I've decided to make a very simple example. So, I have vector, it has structure type. Structure, in its turn, has 3 array: a, b, c. I fill them, and then try to print elements of first array in the structure. But I do something wrong and don't know what exactly, maybe everything. Here is the code:

using namespace std;

struct hl {
    int a [3];
    int b [3];
    int c [3];
};

int main()
{
  vector<hl> vec;
  struct hl he;

  for (int i = 0; i!=3; ++i) {
      int aa = 12;
      int bb = 13;
      int cc = 14;

      he.a[i]= aa+i;
      cout <<"Hello.a["<< i << "]=  "<<he.a[i]<<endl;
      he.b[i]= bb+i;
      he.c[i]= cc+i;
  }

  for (std::vector<hl>::iterator it = vec.begin() ; it != vec.end(); ++it) {
    //print arr.a[n]
  }

  return 0;
}

Answer 1

After the loop that fills the arrays of the structure add the following statement

vec.push_back( he );

and then you can output elements of the first array of the structure that is contained in the vector

for ( int x : vec[0].a ) std::cout << x << ' ';
std::cout << std::endl;

Or you could write

for ( const hl &he : vec )
{
   for ( int x : he.a ) std::cout << x << ' ';
   std::cout << std::endl;
}  

Or you could explicitly use iterators of the vector

for ( std::vector<h1>::iterator it = vec.begin(); it != vec.end(); ++it )
{
   for ( size_t i = 0; i < sizeof( it->a ) / sizeof( *it->a ); i++ )
   {
      std::cout << it->a[i] << ' ';
   }
   std::cout << std::endl;
}

Instead of statement

for ( std::vector<h1>::iterator it = vec.begin(); it != vec.end(); ++it )

you couls also write

for ( auto it = vec.begin(); it != vec.end(); ++it )

Answer 2

You are not adding the element he to the vector. You need to do

vec.push_back(he);

The iteration should look like that:

for(std::vector<hl>::iterator it = vec.begin(); it != vec.end(); ++it) {
    std::cout << it->a[0] << ", " << it->a[1] << ", " << it->a[2] << std::endl;
}

Also, in C++ you don't need to prepend struct/class variable declaration with struct keyword. It's C style. You just need:

hl he;