c++ convert int to cstring

#include<isotream>
#include<string>
using namespace std;

string str = to_string(int);
char cstr[size] = "";
strcat_s( cstr, str.c_str());

#include<isotream>
#include<string>

string str = to_string(int);
char cstr[size] = "";
strcat_s( cstr, str.c_str());