Structures, unions, and enums are fundamental data types in programming with distinct characteristics. Structures allocate separate memory for each field, allowing for the storage of different data types simultaneously. Unions, on the other hand, allocate memory equal to the size of the largest data type defined, meaning all fields share the same memory space, which can lead to more efficient memory usage but limits simultaneous access to only one field. Enums serve as a way to define named integer constants, providing a more organized and readable alternative to using preprocessor directives like #DEFINE. Understanding these differences is crucial for effective memory management and code organization in programming.
