# include < iostream > # include # include The preprocessor searches in an implementation-dependent manner, normally in search directories pre-designated by the compiler/IDE. This means the compiler will search in locations where standard library headers are residing. The header files can be found at default locations like /usr/ include or /usr/local/ include . This method is normally used to include standard library header files. Example: Below is the C++ program to demonstrate ... The < iostream > Header File The iostream header file is part of the C++ standard library, it was first introduced in 1998 and provides the definition of standard Input/Output related streams and functions. By using this header , you can use a standard namespace (std) that represents a group of standard library components, classes, functions, and other identifiers. Example In this example, we use iostream header file to see its standard usage. Before C++ was even standardised, the I/O library was developed as < iostream.h >. However, that header has never been a standard C++ header . Some older compilers continued to distribute the < iostream > header also as < iostream.h >. Use < iostream > because it is guaranteed by the standard to exist. It's worth noting that the only standard headers that end with . h are the C standard library headers. All C++ standard library headers do not end with . h . # include < iostream > The C++ standard library header files, as defined in the standard, do not have . h extensions. As mentioned Riccardo Murri's answer, you will also need to call cout by its fully qualified name std::cout, or have one of these two lines (preferably below your # include directives but above your other code): using namespace std;
