Speedy5 is correct. If your functions are declared above main then there is no need to define a prototype for that function. However, it is good practice to define a prototype for all your functions because it adds clairity to what is available and set one up for a little more portability when you plan to expand your code.
But in a nut he is 100% correct and there is nothing more important than begining to under stand how C/C++ work. The languages are very similar but are also very different and to tackle graphic programming from the get-go will be difficult without a firm understanding of how C/C++ work.
DeadPoet
