What is a Struct in C#?
💡 Concept: Struct
A struct in C# is a value type used to encapsulate small groups of related variables such as coordinates, colors, or complex numbers. Structs are stored on the stack and do not support inheritance.
📘 Quick Intro
Unlike classes, structs are value types, meaning they hold their data directly. They are ideal for lightweight objects and are copied by value when assigned or passed to methods.
🧠 Analogy
Think of a struct like a sealed envelope containing data. When you give it to someone, they receive a complete copy. With a class (reference type), you only give them a reference to a shared box — any changes they make affect the original.
🔧 Technical Explanation
- Structs are value types and are stored on the stack.
- Structs cannot inherit from another struct or class, but can implement interfaces.
- They do not require the use of the
newkeyword for instantiation (but can use it). - Default constructors are not allowed; a parameterless one is auto-generated by the compiler.
- Ideal for representing lightweight, immutable data structures.
🎯 Use Cases
- Storing small sets of related data (e.g., Point, Rectangle, Color).
- Improving performance by reducing heap allocation and garbage collection.
- Creating readonly immutable objects for math or graphics operations.
- Representing a record of data without needing inheritance.
💻 Code Example
public struct Point
{
public int X;
public int Y;
public Point(int x, int y)
{
X = x;
Y = y;
}
public void Display()
{
Console.WriteLine($""Point: ({X}, {Y})"");
}
}
// Usage
Point p1 = new Point(10, 20);
Point p2 = p1; // Creates a copy
p2.X = 30;
p1.Display(); // (10, 20)
p2.Display(); // (30, 20)
❓ Interview Q&A
Q1: What is a struct in C#?
A: A struct is a value type that encapsulates related data fields.
Q2: How is struct memory allocated?
A: Structs are allocated on the stack (usually).
Q3: Can structs inherit from other types?
A: No, structs can't inherit from other structs or classes.
Q4: Can a struct implement interfaces?
A: Yes, structs can implement interfaces.
Q5: Can structs have methods?
A: Yes, structs can contain methods, properties, constructors, etc.
Q6: Is struct reference or value type?
A: Struct is a value type.
Q7: Are structs copied by reference or value?
A: Structs are copied by value.
Q8: Can structs have parameterless constructors?
A: No, C# doesn't allow custom parameterless constructors in structs.
Q9: When should you use a struct?
A: When you need lightweight, immutable data containers.
Q10: Can structs be null?
A: No, unless they are nullable using Nullable<T> or T?.
📝 MCQs
Q1. Where is struct stored in memory?
- Heap
- Stack
- Global memory
- Thread pool
Q2. What is struct in C#?
- A reference type
- A pointer
- A value type
- A sealed class
Q3. Can structs implement interfaces?
- No
- Yes
- Only IDisposable
- Only abstract
Q4. What happens when a struct is copied?
- Reference is copied
- Nothing
- A new copy is created
- It becomes null
Q5. Can structs have constructors?
- No
- Yes, only static
- Yes, with parameters
- Yes, but private only
Q6. Can you inherit from a struct?
- Yes
- No
- Only sealed classes
- Only other structs
Q7. Which of these is a value type?
- Class
- Struct
- Array
- Delegate
Q8. How are structs passed to methods?
- By reference
- By pointer
- By value
- By default constructor
Q9. Can struct fields be private?
- No
- Yes
- Only static
- Only readonly
Q10. Which of these is NOT true for structs?
- They are value types
- They are copied by value
- They support inheritance
- They can implement interfaces
💡 Bonus Insight
Structs are excellent for performance-sensitive code where you want to avoid heap allocation. Always consider whether value semantics make sense for your use case before choosing structs over classes.
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