C Programming - Structures, Unions, Enums - Discussion

Structures, unions and enums are user-defined data types which are used to create new data types.

Structure is a user-defined data type which contains variables of different data types, in structures, memory is allocated to individual variables, which are declared in the structure based on their data type.

Memory shares among the variables which are declared in the structure.
We can access any variable at a time.
The size of the structure is defined as the sum of the sizes of all members which are declared in the structure.
Unions are similar to structures, but in unions, the memory is allocated to all the variables with a maximum size of a data member, which is declared in the union.
Same /single memory shares among all the data members which are declared in the union.
We can only have one data member or variable at a time.

Unions are faster than structures and require less memory than structures.

Enum is user user-defined data type in which assigns integer constants to names for easy reading.

All are user-defined datatypes which allow the user to create their own datatype which can be a combination of int, float, char, etc.

Please, explain about union?

Which is better to use structure or union? Any one explain in detail.

@Kamal.

Linked list: list is a collection of elements. There are 2 ways of maintaining list in computer memory. The first way is to take an array for sorting elements of the list. But arrays have some disadvantage. Insertion and deletion of the element require more processing. The second way is implementing a list in a memory by using a self-referential structure.

Do the outputs for structure & union is same?

Array.
Pointer.
Structure.
Union.
Enum.

Are the user defined or secondary types of data type in C?

Structure mean collection of multiple element that can be of different data types. Definition of union is same of structure but only data element is stored in union variable.

Because the secondary data types are arrays, pointers, structures, union and enum, they are user defined data types All of them let you define new data types.

I can't understand explain clearly.