Explain what are data types that store references to objects in memory, and how they differ from value types.

In C#, data types are divided into value types and reference types.

• Reference types store in a variable not the data itself, but a reference (pointer) to the memory area where the object data is located. Examples: classes (class), strings (string), arrays.

• Value types store data directly in the variable. Examples: structures (struct), enumerations (enum), primitive types (int, bool, etc.).

Differences:

• When assigning, value types copy the data itself, while reference types copy the reference to the object.
• Reference types are placed in managed heap, while value types are usually on the stack or inside other objects.
• Changes in a reference type through one reference are visible through other references to the same object, whereas copies of value types are independent.

Example:

class Person { public string Name; }

struct Point { public int X, Y; }

Person p1 = new Person { Name = "Alice" };
Person p2 = p1; // reference copied
p2.Name = "Bob";
Console.WriteLine(p1.Name); // Outputs "Bob" — both refer to the same object

Point pt1 = new Point { X = 1, Y = 2 };
Point pt2 = pt1; // data copied
pt2.X = 10;
Console.WriteLine(pt1.X); // Outputs 1 — copies are independent