It doesn't have anything to do with printable or non-printable. \ is escape character that you need to use to escape " in a string.
Both declarations are valid and do the same thing:
#include <iostream>
int main()
{
char Hi1[] = { '"' , 'H', 'i', '"' , '\0' };
char Hi2[] = { "\"Hi\"" };
std::cout << Hi1;
std::cout << Hi2;
}
For more information, take a look at String and character literals.