Implement strcpy of in C++ return a char* type of in depth analysis

#include "stdafx.h"
#include <string>
#include <iostream>
using namespace std;
char* strcpy(char *src_str, char *dest_str)
{
 char* dest = dest_str;
 if ((src_str == NULL)||(dest_str == NULL))  //Check pointer validity
 {
  throw "Invalid argument(s)";   //An exception is thrown
 }
 while((*dest_str++ = *src_str++) != '0')  //Copy, including '/0' at the end
 {
  NULL;
 }
 return dest;
}

int _tmain(int argc, _TCHAR* argv[])
{
 char src[] = "Hello,world!";
 char des[13] = {0};
 strcpy(src, des);
 cout << des << endl;
 return 0;
}