What is the difference between int, where I write under using namespace std; and then I write it after int main ( ) { };

Question

I think it has got more difference between that codes.
Under namespace std;

#include <iostream>
using namespace std;
int a,b,c;

int main ()
{}

Inside after int main ()

#include<iostream>
using namespace std;
int main ()
{
int a, b, c;
}