What is the difference between union and struct?

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 .

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.

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).

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.

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.