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Is there a better way to comment the parameters' direction in code?
#define IN
#define OUT

void Add(IN int Para1, IN int Para2, OUT int& Result);

void foo(int i, const std::string& s, std::vector<char>& out_buf);
// i and s are obviously "in" variables, while out_buf could be both,
// but you can easily show that by giving the parameter a proper name.

void Add(/*IN*/ int Para1, /*IN*/ int Para2, /*OUT*/ int& Result);

/*Description : Function for adding the two variables.
        * Returns : Nothing
        * Parameters : Para1 and Para2  are **IN** parameter and
        * Result is an **OUT** parameter
        * @author : <put ur name here>
        */
    void Add(IN int Para1, IN int Para2, OUT int& Result);

void Add(int inPara1,int inPara2,int& outResult);

void Add(
    /* input parameters */
    int Para1,
    int Para2,
    /* output parameters */
    int& Result
);

void f(int x);

void f(const Foo& read_only_foo);

void f(int& x);

ostream& operator<<(ostream& os, const Foo& foo);

// fills the specified list with stuff
void some_list(list<int>& out_list);

// returns a new list filled with stuff
list<int> some_list();