What is the Difference Between Class and Struct in C#?
💡 Concept: Class vs Struct
In C#, both classes and structs are used to define custom data types, but they differ in memory behavior, inheritance, and usage scenarios. Understanding these differences helps choose the right type for a given situation.
📘 Quick Intro
A class is a reference type stored on the heap and supports inheritance. A struct is a value type stored on the stack and is ideal for small, immutable objects. Classes support more complex behaviors like polymorphism.
🧠 Analogy
Imagine a class as a shared apartment building—you give people the address, and they all point to the same place (reference). A struct is like a personal tent—everyone has their own separate tent, even if the setup is similar (value).
🔧 Technical Explanation
- Classes are reference types; structs are value types.
- Classes are stored on the heap; structs on the stack (usually).
- Classes support inheritance and polymorphism; structs do not.
- Structs are better for lightweight, immutable types with short lifespan.
- Modifying a class instance affects all references; modifying a struct affects only that copy.
🎯 Use Cases
- ✅ Use classes when you need inheritance, polymorphism, or reference sharing.
- ✅ Use structs when performance matters and your object is small and immutable.
- ✅ Structs are ideal for value-like types such as coordinates, colors, measurements.
- ✅ Classes are more suited for domain models, services, and complex behaviors.
💻 Code Example
public class Person
{
public string Name;
public void Greet() => Console.WriteLine($""Hello, I am {Name}"");
}
public struct Coordinate
{
public int X, Y;
public Coordinate(int x, int y)
{
X = x;
Y = y;
}
}
// Usage
var p1 = new Person { Name = ""Alice"" };
var p2 = p1;
p2.Name = ""Bob"";
Console.WriteLine(p1.Name); // Bob — same reference
var c1 = new Coordinate(10, 20);
var c2 = c1;
c2.X = 99;
Console.WriteLine(c1.X); // 10 — copied by value
❓ Interview Q&A
Q1: What is the primary difference between class and struct?
A: Class is a reference type, struct is a value type.
Q2: Can structs inherit from classes?
A: No, structs cannot inherit from any type except interfaces.
Q3: Where is a struct stored?
A: On the stack (typically).
Q4: Do structs support polymorphism?
A: No, they don’t support polymorphic behavior.
Q5: Can classes be passed by value?
A: No, classes are always passed by reference.
Q6: Which is faster in terms of memory allocation?
A: Structs are faster for small, frequent allocations.
Q7: Are structs good for mutable objects?
A: No, they're best used for immutable data.
Q8: Can structs have methods?
A: Yes, they can have methods and properties.
Q9: What happens when you assign one class object to another?
A: Both point to the same object.
Q10: Do structs support parameterless constructors?
A: No custom parameterless constructors allowed.
📝 MCQs
Q1. What is the default behavior of struct assignment?
- Shared reference
- Copied by value
- Heap reference
- Inheritance
Q2. Which of these supports inheritance?
- Struct
- Class
- Enum
- All of the above
Q3. Where is a class stored?
- Stack
- Heap
- Register
- Thread
Q4. Can a struct be null?
- Yes
- No
- Sometimes
- Only when static
Q5. Which supports polymorphism?
- Struct
- Class
- Static
- Array
Q6. Can struct fields be initialized inline?
- Yes
- No (before C# 10)
- Only in methods
- Only with readonly
Q7. Is struct a value or reference type?
- Reference type
- Value type
- Dynamic type
- Generic type
Q8. Can class methods be virtual?
- No
- Yes
- Only abstract
- Only static
Q9. Which is more suitable for large objects?
- Class
- Struct
- Enum
- Interface
Q10. Can structs implement interfaces?
- Yes
- No
- Only IDisposable
- Only if abstract
💡 Bonus Insight
Structs avoid GC pressure and are ideal in high-performance scenarios like graphics or games. However, always consider behavior and copying semantics before choosing struct over class.
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