Dynamic array to store strings

#include <string>
#include <iostream>
#include <memory>

int main()

{
std::string s1;
std::string s2;
while(std::cin >> s1 >> s2)
{
   std::string s3 = s1 + s2;
   int size = s3.length();
   std::cout << size <<'\n';
   std::unique_ptr<char[]>ptr(new char[size]);
   for(int i=0; i<size; ++i)
   {
   ptr[i] = (s3.c_str())[i];
   }
   for(int i=0;i<size;++i)
   {
   std::cout << ptr[i];
   }
   break;
}

}

This is an exercise to concatenate two strings and store them in array of char. INitially, I wss having trouble passing int he string into the array. Later, I managed to convert it into c string and pass it into array.

I was wondering is there a better medhtod to deal with it