What is the Difference Between Classes and Structures?

Classes and structures are both user-defined data types that serve as containers for other data types. They are used to group logically related data items of different types together. However, there are several key differences between classes and structures:

1. Data Type: Classes are reference types, while structures are value types. This means that when a class object is created, a reference to its memory location is passed, whereas when a structure object is created, a copy of the structure's data is made.
2. Accessibility: By default, members of a class have private access, while members of a structure have public access. This means that class members can only be accessed within the class itself or derived classes, whereas structure members can be accessed by any part of the code that has access to the structure variable.
3. Memory Allocation: Classes use heap allocation, while structures use stack allocation. This means that class objects are stored in the heap, and memory is allocated and deallocated as objects are created and destroyed. In contrast, structure objects are stored on the stack, with memory being automatically allocated and deallocated as the structure variable goes in and out of scope.
4. Inheritance: Classes can inherit from other classes, but structures cannot. This means that classes can be derived from other classes and have access to their data and methods, while structures cannot.
5. Size and Performance: Classes are typically used for larger, more complex objects, while structures are used for smaller, simpler objects that are used frequently and need to be passed around quickly. The allocation and de-allocation of value types (structures) are cheaper as compared to reference types (classes), and the allocation of large value types is more efficient than the allocation of large reference types.
6. Instance Creation: An instance of a class is called an 'object', while an instance of a structure is called a 'structure variable'.

In summary, classes are more suitable for large, complex objects and offer features like inheritance and polymorphism, while structures are better suited for smaller, simpler objects that need to be passed around efficiently.

Comparative Table: Classes vs Structures

Here is a table comparing the differences between classes and structures:

In summary, the main differences between classes and structures in C# are inheritance, reference type vs value type, default constructor, initialization, and size/performance. Classes are usually used for larger, more complex programs, while structures are used for smaller programs with limited features and performance requirements.