Type conversion and casting in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the difference between implicit and explicit type conversion in C#?

Implicit conversion happens automatically when there is no risk of data loss, like converting an int to a double. Explicit conversion (casting) requires you to specify the type because it might lose data or cause errors, like converting a double to an int.

beginner

How do you perform explicit casting from a double to an int in C#?

You use parentheses with the target type before the value, like this: int number = (int)3.14;. This cuts off the decimal part and keeps only the whole number.

intermediate

What happens if you try to cast an object to an incompatible type using (Type) casting?

You get an InvalidCastException at runtime because the object cannot be converted to that type. You should check the type before casting or use safe casting methods.

intermediate

What is the difference between as operator and regular casting in C#?

The as operator tries to cast an object to a type and returns null if it fails, instead of throwing an exception. Regular casting throws an exception if the cast is invalid.

intermediate

Explain boxing and unboxing in C#.

Boxing is converting a value type (like int) to an object type, wrapping the value inside an object. Unboxing extracts the value type back from the object. Boxing and unboxing can affect performance if overused.

Which of these conversions is implicit in C#?

A double to int

B object to string

C int to double

D string to int

Converting int to double is implicit because it is safe and no data is lost.

What does this code do? int x = (int)5.99;

A Converts 5.99 to 5 by dropping the decimal

B Throws an error

C Rounds 5.99 to 6

D Stores 5.99 as an int

Casting double to int drops the decimal part, so x becomes 5.

What will happen if you cast an object to an incompatible type using (Type) casting?

A Throws InvalidCastException

B Converts silently

C Returns null

D Returns default value

InvalidCastException is thrown when casting fails at runtime.

Which operator returns null instead of throwing an exception when casting fails?

A cast operator (Type)

B as operator

C is operator

D typeof operator

The 'as' operator returns null if the cast is invalid.

What is boxing in C#?

A Converting a reference type to a value type

B Converting a string to a number

C Casting between two reference types

D Converting a value type to an object

Boxing wraps a value type inside an object.

Describe how implicit and explicit type conversions work in C# and when you should use each.

Think about when the computer converts types automatically versus when you must tell it to convert.

Explain boxing and unboxing in C# and why they might affect program performance.

Consider how value types become objects and back.