Question

Can some one please tell me why exactly classes were introduced in C++. Are there some things that classes can perform that cannot be achieved using structures?

Answer 1

Read Stroustrup’s explanation here: What is so great about classes?

A class is the representation of an idea, a concept, in the code. An object of a class represents a particular example of the idea in the code. Without classes, a reader of the code would have to guess about the relationships among data items and functions – classes make such relationships explicit and "understood" by compilers. With classes, more of the high-level structure of your program is reflected in the code, not just in the comments.

A well-designed class presents a clean and simple interface to its users, hiding its representation and saving its users from having to know about that representation. If the representation shouldn’t be hidden – say, because users should be able to change any data member any way they like – you can think of that class as "just a plain old data structure"; for example:

struct Pair {
        Pair(const string& n, const string& v) : name(n), value(v) { }
        string name, value;
};

Note that even data structures can benefit from auxiliary functions, such as constructors.