couple questions......

1. what does using namespace std exactly do?

2. does it do something to the way eof works?
i had a program that worked when i didnt have using namespace std but i needed to add it for other reasons and now it seems like my eof (end of file) doesnt work and my program just goes into an endless loop. i was using eof because i need to keep getting data from a file until it reaches the eof.