I recently learn about the polymorphism and I don't know what is the purpose to use this feature. From http://www.cplusplus.com/doc/tutorial/polymorphism/ , it uses the child class rather than the parent class. I thought most of the time we inherit and we only use the parent class to access the child. Why would he create a pointer of child class and point to parent class then modify the value on the parent inherit class members?
Can I get some example to on using polymorphism?