What is classes in programing?

Answer 1

There are no classes in C; it is not an object-oriented programming language.

C++ has classes. A class is a data type from which objects can instantiated in much the same way that an integer variable can be instantiated from an int data type in both C and C++. However, an int is a primitive data type; it has no member methods associated with it. The built-in operators are designed to operate upon primitive data types but those operators are not integral to the type.

A class is more like a struct in C; an aggregate of data values. A class can contain both static data (data that is common to the class) and non-static data (data that relates to an instance of the class). However, as well as storing data, a class can also define member functions that operate upon that data, but that are scoped to the class (static member functions) or to an instance of the class (instance member functions). Unlike C where a struct's data members are always public, a C++ class can define separate public, protected and private data members (and functions), where private is the default access. A C++ struct is also a class, but one where the members are public by default. As such, a C++ struct can be used to create trivial "plain old data" classes that are compatible with C code as well as to create highly complex data types.

Objects are self-contained entities where the member methods (functions and operators) have private access to the class representation. Non-member functions cannot gain access to this representation other than through public member functions or by being declared a friend of the class. The protected representation is the same as the private representation but is also accessible to derivatives of the class. Derivatives automatically inherit the public and protected members of their base classes, but not the private members. This makes it possible to derive more specialised classes from existing classes without have to duplicate the base class code.