What is include iostream in C++

The #include <iostream> is a preprocessor directive that tells the compiler to include the contents of the <iostream> header file in your C++ program. This header file is a part of the C++ Standard Library and provides input and output functionality, allowing you to work with input and output streams, such as standard input (keyboard) and standard output (console).

The <iostream> header file includes definitions for the following standard C++ stream objects:

1. std::cin: This is the standard input stream object, which is used for reading input from the user or external sources like files.
2. std::cout: This is the standard output stream object, which is used for writing output to the console.
3. std::cerr: This is the standard error stream object, which is typically used for printing error messages to the console.
4. std::endl: This is a special value that represents the end of a line. It’s often used to move to the next line when writing output.

By including <iostream>, you gain access to these stream objects and the various input and output functions provided by the C++ Standard Library, such as std::cin >> variable for input and std::cout << "Hello, World!" for output.

Here’s a simple example of using <iostream> to print a message to the console:

#include <iostream>

int main() {
    std::cout << "Hello, World!" << std::endl;
    return 0;
}

In this code, <iostream> is included, and std::cout is used to print “Hello, World!” followed by a newline to the console.