Explain the difference between value types and reference types in C#.

Value Types:

• Stored directly on the stack (or inline in containing types)
• Contain the actual data directly
• Each variable has its own copy of the data
• When you copy a value type, you copy the actual data
• Examples: int, double, bool, struct, enum, decimal, DateTime
• Derive from System.ValueType
• Cannot be null (unless nullable value type like int?)

Reference Types:

• Stored on the heap
• Variable contains a reference (pointer) to the actual data
• Multiple variables can reference the same object
• When you copy a reference type, you copy the reference, not the data
• Examples: class, interface, delegate, string, object, arrays
• Derive from System.Object
• Can be null

Key Differences Illustrated:

Value Type Example:

int a = 10;
int b = a;  // Creates a COPY of the value
b = 20;
Console.WriteLine(a);  // Output: 10 (unchanged)
Console.WriteLine(b);  // Output: 20

Reference Type Example:

class Person { public string Name { get; set; } }

Person person1 = new Person { Name = "John" };
Person person2 = person1;  // Copies the REFERENCE, not the object
person2.Name = "Jane";

Console.WriteLine(person1.Name);  // Output: "Jane" (changed!)
Console.WriteLine(person2.Name);  // Output: "Jane"
// Both variables point to the same object in memory

Memory Allocation:

• Value types are typically faster to allocate/deallocate (stack allocation)
• Reference types require heap allocation and garbage collection
• Value types have less memory overhead (no object header)

Performance Implications:

• Use value types for small, simple data structures
• Use reference types when you need shared references or large data
• Boxing occurs when converting value type to reference type (performance cost)