Casting with as and is operators in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the as operator do in C#?

The as operator tries to cast an object to a specified type. If it fails, it returns null instead of throwing an error.

beginner

How does the is operator work in C#?

The is operator checks if an object is of a certain type and returns true or false.

beginner

What happens if you use as to cast an incompatible type?

Instead of causing an error, as returns null when the cast is not possible.

intermediate

Can is operator be used to safely cast an object?

No, is only checks the type and returns a boolean. To cast safely, combine is with a cast or use as.

beginner

Show a simple example of using as and is operators.

Example:<br>

object obj = "hello";
string s1 = obj as string; // s1 = "hello"
if (obj is string s2) {
  // s2 is "hello"
}

What does the as operator return if the cast fails?

A zero

B throws an exception

C false

D null

The as operator returns null if the cast is not possible, avoiding exceptions.

Which operator checks if an object is a certain type and returns a boolean?

A is

B as

C cast

D typeof

The is operator returns true or false depending on the object's type.

What is the result of obj as string if obj is an integer?

A null

B integer value

C throws exception

D true

Casting an integer to string with as returns null because the types are incompatible.

How can you safely cast an object after checking its type with is?

A Use <code>as</code> operator

B Use <code>typeof</code>

C Use explicit cast after <code>is</code> check

D Use <code>new</code> keyword

After confirming type with is, you can safely cast using explicit cast syntax.

Which operator is better to avoid exceptions when casting?

A is

B as

C explicit cast

D typeof

The as operator returns null instead of throwing exceptions, making it safer.

Explain how the as and is operators help with type casting in C#.

Think about how to safely convert or check types without crashing your program.

Describe a scenario where using as is better than an explicit cast.

Consider when your program needs to keep running even if the cast is not possible.