What are classes and objects in Cpp?

Answer 1

A class is the definition of an user-defined type while an object is an instance of a class.

class foo {}; // definition of a type (implementation omitted for brevity).

struct bar {}; // another definition of a type

foo x; // x is an instance of the foo class, therefore x is an object

bar y; // y is an instance of the bar class, therefore y is an object

Note that in C++, struct and class are exactly the same (they are both classes), the only difference being that members of a class are private by default while members of a struct are public by default. Thus the following definitions are exactly the same:

struct X {

Y(){} // public by default

};

class Y {

public:

X(){} // public by specification

};

As are the following:

struct A {

private:

int m_data; // private by specification

};

class B {

int m_data; // private by default

};

Answer 2

Because if we didn't need classes or objects then we'd use C instead. Note that an object is simply an instance of a class. Classifying our data objects makes it much easier to develop highly complex data structures than with C alone, because each object is a self-contained capsule that is entirely responsible for its own data. Encapsulating data and the methods that operate upon that data is one of the four fundamentals of object-oriented programming. The other three are abstraction, inheritance and polymorphism. C alone has none of these fundamentals, thus programming in C is much more complex than in C++. By the same token, C++ is every bit as efficient as C, but is many times easier to work with.