Value type vs reference type performance in C Sharp (C#) - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of struct vs class assignment

Consider the following C# code. What will be the output when it runs?

C Sharp (C#)

struct PointStruct { public int X; public int Y; }
class PointClass { public int X; public int Y; }

var ps1 = new PointStruct { X = 5, Y = 10 };
var ps2 = ps1;
ps2.X = 20;

var pc1 = new PointClass { X = 5, Y = 10 };
var pc2 = pc1;
pc2.X = 20;

Console.WriteLine($"ps1.X = {ps1.X}, ps2.X = {ps2.X}");
Console.WriteLine($"pc1.X = {pc1.X}, pc2.X = {pc2.X}");

A

ps1.X = 20, ps2.X = 20
pc1.X = 5, pc2.X = 20

B

ps1.X = 5, ps2.X = 20
pc1.X = 20, pc2.X = 20

C

ps1.X = 5, ps2.X = 5
pc1.X = 5, pc2.X = 5

D

ps1.X = 20, ps2.X = 5
pc1.X = 20, pc2.X = 5

💡 Hint

Remember that structs are value types and classes are reference types.

Structs are copied by value, so changing ps2.X does not affect ps1.X.

Classes are copied by reference, so changing pc2.X also changes pc1.X.

❓ Predict Output

intermediate

Performance difference in method calls

What is the expected output of the following C# program that measures elapsed time for method calls on value and reference types?

C Sharp (C#)

struct MyStruct { public int Value; public void Increment() => Value++; }
class MyClass { public int Value; public void Increment() => Value++; }

var s = new MyStruct();
var c = new MyClass();

var sw = System.Diagnostics.Stopwatch.StartNew();
for (int i = 0; i < 10000000; i++) s.Increment();
sw.Stop();
var structTime = sw.ElapsedMilliseconds;

sw.Restart();
for (int i = 0; i < 10000000; i++) c.Increment();
sw.Stop();
var classTime = sw.ElapsedMilliseconds;

Console.WriteLine($"Struct time: {structTime} ms");
Console.WriteLine($"Class time: {classTime} ms");

A Struct time: less than Class time

B Program throws a runtime exception

C Struct time: equal to Class time

D Struct time: greater than Class time

💡 Hint

Value types avoid heap allocation and indirection, which can improve performance.

Struct method calls are generally faster because they avoid heap allocation and pointer dereferencing.

Class method calls involve reference indirection and possible heap overhead.

🔧 Debug

advanced

Why does this struct cause unexpected behavior?

Examine the following code. Why does the output show unexpected values for the struct fields after modification?

C Sharp (C#)

struct Data {
  public int A;
  public int B;
  public void Update() {
    A = 10;
    B = 20;
  }
}

Data d = new Data();
d.Update();
Console.WriteLine($"A = {d.A}, B = {d.B}");

Data d2 = d;
d2.A = 30;
Console.WriteLine($"d.A = {d.A}, d2.A = {d2.A}");

A Because the struct fields are private and cannot be changed

B Because structs are reference types, d2 and d refer to the same object

C Because Update() method does not modify the struct fields

D Because structs are value types, d2 is a copy; modifying d2.A does not affect d.A

💡 Hint

Think about how value types behave when assigned to new variables.

Structs are copied on assignment, so d2 is a separate copy of d.

Changing d2.A does not affect d.A.

📝 Syntax

advanced

Identify the syntax error in struct initialization

Which option contains the correct syntax to initialize a struct with fields X=1 and Y=2?

C Sharp (C#)

struct Point { public int X; public int Y; }

A var p = new Point { X = 1, Y = 2 };

B var p = Point(1, 2);

C var p = new Point(1, 2);

D var p = new Point[X=1, Y=2];

💡 Hint

Structs can be initialized with object initializer syntax.

Option A uses correct object initializer syntax.

Options B and C are invalid because Point has no constructor defined.

Option A uses invalid syntax.

🚀 Application

expert

Choosing between struct and class for performance

You need to store millions of small 2D points with integer coordinates and perform many calculations. Which choice is best for performance and why?

A Use class because it is faster to copy than struct

B Use class because it allows inheritance and polymorphism

C Use struct because it stores data inline and reduces heap allocations

D Use struct because it is always faster regardless of size

💡 Hint

Think about memory layout and allocation overhead.

Structs store data inline, reducing heap allocations and improving cache locality.

Classes have overhead due to heap allocation and references.

Inheritance is not needed here.