Exercise 1: Adding Operators to the Point class
By supporting operators, you can make your classes easier and more natural to use. However you must not “overuse” operators. Only use operators if the functionality of the operator is clear without reading documentation. Thus adding mathematical operators to a complex number class is good but using a + operator with a double as an argument on a point to increase the x-coordinate is questionable. So use operators with care. In this exercise we add a few operators to the Point class. Most operators do not change the original objects but return the result as a new object. Normally only the = operator and += and variants change the original object. Add the following operators:

Exercise 2: Ostream << Operator
It would be nice if you could send a point or a line directly to the cout object without calling the ToString() method, just as with the primitive types. This is possible by adding a << operator function that has on the left an std::ostream and on the right the point or line object. Since you can’t add a member function to the std::ostream class, you have to create it as a global function (outside the class definition, but inside the class header file):
ostream& operator << (ostream& os, const Point& p); // Send to ostream.
The implementation uses the << operator to send data to the os input argument. Since it is a global function, you can’t access the private members of Point. To simplify things, you can use the ToString() method of Point to get the string to send to the os argument. Also create a similar << operator for printing lines (and circles if you made a circle class). Adapt the test program to test the << operator for points and lines.

Exercise 3: Constructors as conversion operator
In this exercise we are going to do a little experiment. First add to the Point class a constructor that accepts one double as an argument. The implementation should set both the x- and y-coordinate to this value. Next try the following code in the test program:
Point p(1.0, 1.0);
if (p==1.0) cout<<“Equal!”<<endl;
else cout<<“Not equal”<<endl;
Will this code compile and can you explain why? It turns out that the Point constructor with the single double argument is implicitly used to convert the number in the if statement to a Point object. Thus constructors are used as implicit conversion operators. To prevent the usage of constructors are implicit conversion operators, declare the constructor as explicit:
explicit Point(double value);
Now try to compile the program again and you will see that now the if statement gives a compiler error. You can still use the constructor as conversion operator but then explicitly:
if (p==(Point)1.0) cout<<“Equal!”<<endl;

Exercise 4: Friends
Normally, only member functions of a class can access the private members of that class. Global functions and other classes can’t access the private members of that class. You can make an exception on that rule by declaring certain functions or classes as friend. For example the << operator for sending the point or line to the std::ostream class had to be a global function and thus can’t access the private members. Move the << operator of Point and Line inside the class definition and declare it as friend. The function remains a global function but it can now access the data members directly without the need for calling the getters or ToString() function. Normally, friends are to be avoided because it violates the data hiding principle. But in case of global operator functions it makes sense because you would actually want to make those global operator functions as member function but this was not possible.