String type and immutability in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean that strings are immutable in C#?

It means once a string is created, it cannot be changed. Any modification creates a new string instead of changing the original.

beginner

How do you create a new string by changing part of an existing string?

You create a new string by using methods like Replace, Substring, or concatenation. The original string stays the same.

intermediate

Why is string immutability useful in programming?

It helps avoid unexpected changes, makes programs safer, and allows strings to be shared safely across different parts of a program.

intermediate

What happens in memory when you modify a string in C#?

A new string object is created in memory with the changes, and the old string remains unchanged until garbage collected.

beginner

Which C# type is immutable: String or StringBuilder?

String is immutable, while StringBuilder is mutable and allows changes without creating new objects.

What happens when you call Replace on a string in C#?

A A new string is created with the replacements.

B The original string is changed directly.

C An error occurs because strings cannot be changed.

D The string is deleted.

Calling Replace returns a new string with changes; the original string stays the same.

Why are strings immutable in C#?

A To improve safety and performance by preventing accidental changes.

B Because strings are stored in a special file.

C To allow strings to be changed faster.

D Because C# does not support changing strings.

Immutability helps avoid bugs and allows safe sharing of strings.

Which type should you use for many string changes to improve performance?

A int

B String

C StringBuilder

D char

StringBuilder allows efficient modifications without creating new strings each time.

If you do this: string s = "cat"; s += "s"; what happens?

A The original string "cat" changes to "cats".

B A new string "cats" is created and s points to it.

C An error occurs because strings cannot be changed.

D The string s becomes null.

The += operator creates a new string and assigns it to s.

Which statement is true about string immutability?

A Strings can be changed directly.

B Strings are stored as arrays of integers.

C Strings are mutable by default.

D Strings cannot be changed after creation.

Strings in C# are immutable, meaning they cannot be changed after creation.

Explain what string immutability means and why it is important in C#.

Think about how changing a string actually works behind the scenes.

Describe the difference between String and StringBuilder in terms of mutability.

Consider performance when changing strings many times.