Which of the following is not a keyword in C++?

The term "constant" is not a keyword in C++. In C++, keywords are reserved words that have specific meanings and functionalities defined by the language itself, which the programmer cannot use for other purposes.

On the other hand, "goto," "delete," and "break" are keywords. "Goto" allows for a jump to a labeled statement within a function, often considered controversial due to its potential to make code flow hard to follow. "Delete" is used to deallocate memory that was previously allocated with "new," and "break" is used to exit from a loop or switch statement prematurely.

Understanding the use and definition of these keywords is crucial for writing effective C++ code, as using them correctly ensures that the program behaves as intended. Recognizing that "constant" is not a built-in keyword helps clarify that it may be used in a different context, such as in defining constant variables or using the const qualifier, but it does not have special syntax or functionality on its own in the way that reserved keywords do.