using namespace std; question.

What is

Code:

---

using namespace std;

---

and should I use it?

It makes the namespace for the block that follows...
You can use it like this:

Code:

---

#include <iostream>
using namespace std;

int main()
{
    cout << "Hi" << endl;
    return 0;
}

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so you don't need to use std::cout, and std::endl; each time in your program...

Check this out