C :: Passing Values To A Function Error

I'm working through the Let us C book. One exercise asks me to collect int and float , then pass them to a function that gets product of these and returns it to main. My code looks like this:

Code:

#include <stdio.h>#include <stdlib.h>
main()
{
int a;
float b, c;

[Code]...

So while compiling i get an error about conflicting types for product. I tried to google that error but couldn't understand what's the problem. My only clue is that i can't pass int and float to a function at the same time... Could that be it?