What is the difference between union and struct?

A structure is a user-defined data type available in C that allows to combining data items of different kinds. Structures are used to represent a record. A union is a special data type available in C that allows storing different data types in the same memory location.

Basically struct is used to define a structure. But when we want to use it we have to use the struct keyword in C. If we use the typedef keyword, then a new name, we can use the struct by that name, without writing the struct keyword .

typedef is a reserved keyword in the programming languages C and C++. It is used to create an additional name (alias) for another data type , but does not create a new type, except in the obscure case of a qualified typedef of an array type where the typedef qualifiers are transferred to the array element type.

The typedef specifier cannot be combined with any other specifier except for type-specifiers . The typedef-names are aliases for existing types, and are not declarations of new types. Typedef cannot be used to change the meaning of an existing type name (including a typedef-name).

The keyword Typedef is used to give a new symbolic name for the existing name . Typedef is type definitions make code more readable by giving application-specific names to types. In this example, we will create type definition with structures. The name of type definition of a structure is usually in upper case letters.

Conclusion: typedef is not compulsory to use . Basically, it is used to reduce the complexity of declaration as well as it gives you the freedom to choose the name of your interest of data type.