Casting with as and is operators in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of casting with 'as' operator

What is the output of this C# code snippet?

C Sharp (C#)

class Animal {}
class Dog : Animal {}

Animal a = new Animal();
Dog d = a as Dog;
Console.WriteLine(d == null ? "null" : "not null");

A null

B not null

C Compilation error

D Runtime exception

💡 Hint

The 'as' operator returns null if the cast fails instead of throwing an exception.

The variable 'a' is an Animal instance, not a Dog. Using 'as' to cast to Dog returns null because 'a' is not a Dog or derived from Dog.

❓ Predict Output

intermediate

Using 'is' operator with inheritance

What will this C# code print?

C Sharp (C#)

class Vehicle {}
class Car : Vehicle {}

Vehicle v = new Car();
Console.WriteLine(v is Car);

A Runtime exception

B True

C Compilation error

D False

💡 Hint

The 'is' operator checks if the object is compatible with the given type.

The variable 'v' refers to a Car instance, so 'v is Car' returns true.

🔧 Debug

advanced

Why does this cast cause a runtime error?

Consider this code snippet. Which option explains why it throws an exception?

C Sharp (C#)

object obj = "hello";
int num = (int)obj;

A The cast fails because 'obj' is a string, not an int, causing InvalidCastException.

B The 'as' operator returns null, so 'num' is zero.

C The code compiles but prints 'hello'.

D The 'is' operator should be used instead of cast.

💡 Hint

Direct casting throws an exception if types are incompatible.

Casting a string object to int directly causes InvalidCastException at runtime.

❓ Predict Output

advanced

Result of 'as' operator with value types

What happens when you run this C# code?

C Sharp (C#)

object o = 5;
int? n = o as int?;
Console.WriteLine(n.HasValue ? n.Value.ToString() : "null");

A Compilation error

B null

C 5

D Runtime exception

💡 Hint

Nullable types can be used with 'as' operator.

The 'as' operator can cast boxed value types to nullable types, so 'n' has value 5.

🧠 Conceptual

expert

Difference between 'is' and 'as' operators

Which statement correctly describes the difference between 'is' and 'as' operators in C#?

A 'is' throws exception on failure; 'as' returns default value.

B 'is' performs casting and returns null if it fails; 'as' checks type and returns bool.

C 'is' and 'as' are interchangeable and behave the same.

D 'is' checks type compatibility and returns a bool; 'as' attempts cast and returns null if it fails.

💡 Hint

Think about what each operator returns when the cast is not possible.

'is' returns true or false depending on type compatibility; 'as' returns the casted object or null if cast fails.