The point in ANSI prototypes is that when you use them, any call to the function will actually convert the parameters to whatever type the prototye says.

More clearly, the K&R style declaration of arguments (which is not a prototype btw) say only what the function pops off the stack, but not what the caller pushes to the stack. If, however, a function has an ANSI C prototype (and it's included in wherever you call the function from), the C compiler will automatically convert parameters to whatever the prototye says, and will warn you if you call the function with an incompatible number or type of parameters.