When declaring functions, what must be specified if not declared as void?

When declaring functions in programming languages, if the function is not declared as 'void', it is essential to specify the return type along with the function name. The return type indicates what kind of value the function will return when it is called. This is crucial for the compiler and for other developers to understand how to correctly use the function and what to expect from it.

If the function is intended to return a specific type, such as an integer or a string, this requires a clear declaration. For example, in a language like C or C++, a function that returns an integer would be declared with 'int' as the return type, followed by the function name.

Not providing the specified return type can lead to ambiguity and errors in the program, as the calling code might not know how to handle the return value appropriately. The function name is also necessary because it is how the function can be invoked later, but the return type is fundamental in defining the function’s contract with the rest of the code. The parameters of the function are important as well but do not replace the need for the return type in the declaration.