Structures and Unions Introduction: Structures and unions are composite data types in C that allow the grouping of multiple variables of different data types under a single name. They provide a way to represent complex data structures in a program, making it easier to organize and manipulate data. Definition: Structure: A structure is a collection of variables (of different data types) grouped together under a single name. Each variable within a structure is called a member or field. Structures enable the creation of custom data types to represent real-world entities. They are defined using the struct keyword. Union: A union is similar to a structure in that it also groups variables of different data types under a single name. However, unlike structures, unions allocate memory that is only as large as the largest member. This means that only one member of the union can be accessed at a time. Unions are useful when memory conservation is a concern, and only one member needs to b...