I had explained Built-in and Derived Data types in previous blogs. Now, Let's resume our topic from User Defined Data types. Simple definition - User defined data types are the data types which the User define by himself/herself. We need these data types because there are certain cases when the pre-defined data types won't help us, e.g. think of a list, which contain every information about every particular student learning in a school. Like Student name, Student IDs, Student class, Student section etc. You can think of using arrays, but arrays can only contain one field of data of built-in datatypes like int, char etc. Which is not sufficient. Now, We will discuss the following topics - Class. Structures. Enumeration. Union. So, let's start our discussion. Classes Class is a data type present in C++, but not in C. Classes can be considered as a mechanism that allows us to create new types(of data), and we can declare and use objects of that type. A class definition cons...