The inclusion of a name for each argument as in the definition of a standard function is optional, although recommendable. 1030 Number is even. 0 Number is even. This example is indeed not an example of effectiveness, I am sure that at this point you can already make a program with the same result using only the half of code lines. But this example ilustrates how protyping works.
Many programmers recommend that all functions be prototyped.
It is also my recommendation, mainly in case that there are many functions or in the case that these are very long, since, having the prototype of all the functions in the same place can spare us some time when consulting how to call it or even ease the creation of a header file. String of characters.