What does the `throw` keyword do in C++?

The throw keyword in C++ is used to signal that an exception has occurred. When an error or unexpected behavior is detected in the program, the throw statement allows you to generate an exception object that represents the error condition. This exception can then be caught and handled by surrounding code that is set up with a try block and a corresponding catch block.

This mechanism is part of C++'s exception handling framework, providing a way to separate error handling logic from regular code. By using throw, you can effectively manage error conditions and allow a program to continue running or to terminate gracefully by managing exceptional situations in a controlled manner.

In contrast, the other options refer to different functionalities in C++. For instance, defining a new variable type is accomplished through type declaration, not the throw keyword. Similarly, indicating the end of a function is done using a return statement, while initiating a loop structure requires keywords like for, while, or do. Understanding the specific role of throw helps clarify how C++ manages exceptions and why it is a critical part of robust programming practices.