A union in C programming is a user defined data type which may hold members of different sizes and type. Union uses a single memory location to hold more than one variables. However, only one of its members can be accessed at a time and all other members will contain garbage values. A structure is a convenient tool for handling a group of logically related data items. Structure help to organize complex data is a more meaningful way. It is powerful concept that we may after need to use in our program Design.