Which header file provides definitions for the cin and cout objects?

The correct answer is that the header file iostream provides definitions for the cin and cout objects. In C++, iostream is specifically designed for input and output operations, where cin is used for standard input, typically from the keyboard, and cout is used for standard output, usually to the console. This header file includes the necessary components to enable these objects to function properly, as well as to facilitate the flow of data between the program and the system's I/O devices.

Other header files have different purposes: fstream is used for file handling operations, enabling programs to read from and write to files; iomanip is used for input/output manipulators that assist in formatting output, but does not include definitions for cin and cout; cstdio is a C-style header for input and output functions but does not define C++ specific objects such as cin and cout. Therefore, iostream is essential for any program that requires standard input and output operations in C++.