function arguments()

Which do you prefer:


int foo(int a);
int foo(int a = someDefaultArgument);

or

int foo(int a);
int foo(void);

Let's try something:
I am using a library with this function.
int foo( int a = 3, int b = 5 );
- I'd really like to specify b as 6.
- I also really need to use the default value for a.
- I don't know the default value for a.
- All numbers are valid inputs for each argument.
Question: How do I call this function?