In programming, a declaration of a function to the compiler indicating what types of parameters are passed to it and what value is returned. The compiler can then report an error if a function within the program is not written to conform to the prototype. See function.

The following C example is the simplest prototype. The function displays "Hello World" on screen without receiving any parameters or returning any values to the calling instruction. "Void" means "nothing."

         Prototype
         void printHelloWorld(void);


         Function
         void printHelloWorld(void)
         {
         printf ("Hello World\n");
         }

Prototypes can be much more complicated as in this C example where five parameters are passed to a graphics function.

  void   DrawTransparentBitmap(HDC hdc,
                HBITMAP hBitmap,
                int xStart,
                int yStart,
                COLORREF cTransparentColor);