Performance implications of boxing in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of boxing with value types

What is the output of this C# code snippet involving boxing and unboxing?

C Sharp (C#)

int x = 10;
object o = x; // boxing
int y = (int)o; // unboxing
Console.WriteLine(y + 5);

A 10

B 15

C Runtime error

D Compilation error

💡 Hint

Remember that boxing copies the value type into an object and unboxing extracts it back.

Boxing copies the integer value 10 into an object. Unboxing extracts the integer back. Adding 5 results in 15.

❓ Predict Output

intermediate

Effect of boxing on performance counters

What will be printed by this code that counts boxing operations?

C Sharp (C#)

int count = 0;
object Box(int x) { count++; return x; }

int a = 5;
object o1 = Box(a);
object o2 = Box(a + 1);
Console.WriteLine(count);

A 2

B 1

C 0

D Compilation error

💡 Hint

Each time an int is assigned to object, boxing occurs.

Both calls to Box receive an int and return an object, so boxing happens twice, incrementing count twice.

🔧 Debug

advanced

Identify the performance issue caused by boxing

Which line in this code causes boxing and may degrade performance?

C Sharp (C#)

List<int> numbers = new List<int> {1, 2, 3};
foreach (object obj in numbers) {
    Console.WriteLine(obj);
}

A List<int> numbers = new List<int> {1, 2, 3};

B Console.WriteLine(obj)

C No boxing occurs

D foreach (object obj in numbers)

💡 Hint

Check the type used in the foreach loop variable.

The foreach uses object to iterate over a List. Each int is boxed to object causing performance overhead.

❓ Predict Output

advanced

Output when boxing affects method overload resolution

What is the output of this code involving method overloads and boxing?

C Sharp (C#)

void Print(int x) { Console.WriteLine("Int: " + x); }
void Print(object o) { Console.WriteLine("Object: " + o); }

int val = 7;
Print(val);

A Object: 7

B Runtime error

C Int: 7

D Compilation error

💡 Hint

Method overload resolution prefers exact type matches over boxing.

The Print(int) method is chosen because it matches the argument type exactly, avoiding boxing.

🧠 Conceptual

expert

Why does boxing impact performance negatively?

Which of the following best explains why boxing can degrade performance in C#?

A Boxing creates a new object on the heap and copies the value, causing extra memory and CPU overhead.

B Boxing allows direct modification of the original value type, improving speed.

C Boxing converts a value type to a reference type without copying, so it uses less memory.

D Boxing compiles the code to machine language, which slows down execution.

💡 Hint

Think about what happens when a value type is boxed.

Boxing copies the value type into a new object on the heap, which uses more memory and CPU time, slowing performance.