What is a function prototype?

A function prototype is a declaration that provides essential information about a function before it is used in the program. This declaration includes the function's return type, the name of the function, and the types and order of any parameters it takes. By providing this information, the function prototype ensures that the compiler understands how to properly call the function and what to expect in terms of return values and arguments.

Having a prototype allows for better organization and modularization in code, as it enables the function to be defined after its first use. This is particularly helpful when the function is defined in a separate file or follows after its usage in the code, ensuring that the programmer can still implement the logic without facing compilation errors.

The other possibilities do not accurately define a function prototype. For instance, a complete definition of a function includes the detailed implementation, which goes beyond just the prototype. Similarly, a runtime error pertains to errors that occur while the program is running, and a comment about a function does not provide any technical information or structure required for compiler understanding.