Functions Review 

    void fun() {                 
        cout << "A";
    }


    void fin() {
        cout << "B";
        fun();
        cout << "C";
        fun();
    }


    int main() {
        fin();
        fun();          What is the output? ___________________
    }


In the previous code, how many function calls (ignore cout!) _____

                      how many function definitions? ______


Order of definitions -  Call must follow the definition!  

    void fun() {
        
    }

    void fin() {

        fun();     OK? ____

        fan();     OK? ____
    }

    void fan() {

    }

Prototype = first line of a function (return type, name, param's) 

    int fun(int x, double y) {
        if (y > 0)
            return x;
        else 
            return -x;
    }

Prototype is:  ________________________________________  
        

Alternative approach to function definition order:


    void fun();    // start with prototype of each function
    void fin();
    void fan();

    void fun() {   // then give function bodies in any order
        
    }

    void fin() {

        fun();      OK? _____

        fan();      OK? _____
    }

    void fan() {

    }


More simply, skip prototypes and put main at the bottom.


In a call, parameters must match number, type, order.

     (except conversions between int double char bool)


 void fun(int i, double d, bool b, char c) {
      cout << i << " " << d << " " 
           << b << " " << c << endl;
 }

 int main() {
      fun(true, 45, 'H', 72.13);    // works!
 }


Not everything converts!

     fun(int arr[MAX], double x, double y);

     int main() {
         int n;
         double f1, f2;
         int nums[MAX];

         fun(f1,nums,f2);   OK? _____

         fun(nums,f1,f2);   OK? _____

         fun(f1,f2);        OK? _____

     }



Parameters - reference vs. value
      value - just a COPY of caller's data
      reference - sharing the caller's ORIGINAL data

void fun(int a) {     a is:  value or reference
    a = 2 * a;
}

int main() {
    int m = 100;
    fun(m);
    cout << m;        output? ____________
}

----------------------------------------------------------


void fun(int a) {    a is:  value or reference
    a = 2 * a;
}

int main() {
    int m[MAX];
    m[0] = 100;
    fun(m[0]);
    cout << m[0];       output? _____________
}

---------------------------------------------------------

Most parameters are value  (int double char bool)
BUT Arrays are always reference parameters.
(In C/C++, array parameters are NOT copied.)

void fun(int a[MAX]) {     
    a[0] = 2 * a[0];
}

int main() {
    int m[MAX];
    m[0] = 100;
    fun(m);       output? ______________
    cout << m[0];
}


--------------------------------------------------------

Sending arrays (or array elements) as parameters

void fun(int m) {
   ....


int main() {
   int arr[MAX];
   
   fun(arr);       good call? _____

   fun(arr[0]);    good call? _____

-----------------------------------

void fun(int m[MAX]) {
   ....


int main() {
   int arr[MAX];
   
   fun(arr);      good call? ______

   fun(arr[0]);   good call? ______

---------------------------------------------


Declarations in the call or in the definition.


void fun(int a, int b) {
    ....
}

int main() {
    int x = 5;
    int y = 6;
    fun(int x,int y);      Problems? ______________________________
}