1. Review of Function Overloading
Allows different functions to have the same name if they have different types or numbers of arguments, e.g.
int sqr(int x) { return x*x; }
double sqr(double x) { return x*x; }
double sqr(double x, double y) { return x*y; }
int i = 2; double x = 1.2, y = 2.0;
cout << sqr(i) << “ ” << sqr(x) << “ “ << sqr(x,y);

2. Operator Overloading
This is a powerful C++ feature that allows the use of operators for user defined classes, e.g.
dVector A, B, C, D; // a user defined class
C = A + B; // = and + is overloaded
D = A*B; // * is overloaded (dot product)
cout << D; // << is overloaded
Similar to function overloading except it uses operators

3. Member Operator Functions
General form:
return-type class-name::operator#(argument-list)
{ // operation to be performed }
e.g.
void dVector::operator=(dVector &v2) { // v1 = v2
int i;
if ( n1 != v2.n1 || n2 != v2.n2 ) return; // error !
for ( i = n1; i <= n2; i++ ) e(i) = v2.e(i); // copy elements }

4. Improved = Operator
dVector dVector::operator=(dVector &v2) { // v1 = v2
int i;
dVector *ans; // declare a return variable
ans = new dVector(n1,n2); // allocate a dVector
if ( n1 != v2.n1 || n2 != v2.n2 ) return *ans; // error !
for ( i = n1; i <= n2; i++ )
ans->e(i) = e(i) = v2.e(i); // copy elements
return *ans; }

5. Overloading the + Operator
dVector dVector::operator+(dVector &v2) { // v1 + v2
int i;
dVector *ans; // declare a return variable
ans = new dVector(n1,n2); // dynamically allocate
if ( n1 != v2.n1 || n2 != v2.n2 ) return *ans; // error !
for ( i = n1; i <= n2; i++ )
ans->e(i) = e(i) + v2.e(i); // copy elements
return *ans; }

6. Overloading Unary Operators
Example: Norm operator
double dVector::operator!() {
int i;
double ans=0.0; // declare a return variable
for ( i = n1; i <= n2; i++ ) ans += e(i)*e(i);
return sqrt(ans); }

7. Friend Functions
A Friend function is not a member function of a class, but it has access to all its private members, e.g.
class number {
double x; // private member
public:
number() { x = 7.11; } // constructor
friend void show_x(number n); };
void show_x(number n) { cout << n.x; }
number n1; show_x(n1);  7.11;

8. << Operator Overloading
class dVector {
friend ostream &operator<<(ostream &stream, dVector &v);
… };
ostream &operator<<(ostream &stream, dVector &v) {
// example usage: cout << v1 << v2 << v3;
int i;
for ( i = v.n1; i <= v.n2; i++ ) stream << "\n" << v.e(i);
return stream; }