[c++] The #include<iostream> exists, but I get an error: identifier "cout" is undefined. Why?

I learn C++ and COM through the books. In the IDE MS Visual Studio 2012 I have created new empty C++ project, and added some existing files to it. My CPP file contains #include<iostream> row, but in editor I got such messages:

Error: identifier "cout" is undefined

end

Error: identifier "endl" is undefined

Screen:

Why it happens?

The problem is the std namespace you are missing. cout is in the std namespace.
Add using namespace std; after the #include

You can add this at the beginning after #include <iostream>:

using namespace std;

cout is in std namespace, you shall use std::cout in your code. And you shall not add using namespace std; in your header file, it's bad to mix your code with std namespace, especially don't add it in header file.