Why u are using namespace and only iostream instead of iostream.h?

Answer 1

iostream.h would a c version (and does not exist) if you look in the file system the file is iostream without any extension.

Answer 2

namespace is used to save typing std::cout and std::endl
you can leave namespace out if you use std::cout everywhere you normally use cout. there are lots of other functions in std name space that would need std:: in front.