Immutable variables in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean when a variable is immutable in Rust?

An immutable variable is one whose value cannot be changed after it is set. Once assigned, you cannot modify it.

beginner

How do you declare an immutable variable in Rust?

By default, variables declared with <code>let</code> are immutable. For example: <code>let x = 5;</code> creates an immutable variable <code>x</code>.

beginner

What happens if you try to change the value of an immutable variable in Rust?

The Rust compiler will give an error and prevent the program from compiling because immutable variables cannot be changed.

beginner

How can you make a variable mutable in Rust?

You add the keyword <code>mut</code> when declaring the variable, like <code>let mut x = 5;</code>. This allows you to change <code>x</code> later.

intermediate

Why does Rust use immutable variables by default?

Immutable variables help prevent bugs by avoiding accidental changes. They make code safer and easier to understand.

In Rust, what keyword do you use to declare a variable that can be changed?

A var

B let

C mut

D change

The keyword mut makes a variable mutable, allowing its value to be changed.

What will happen if you try to assign a new value to an immutable variable in Rust?

A The compiler will give an error.

B The old value will be kept and the new value ignored.

C The variable will automatically become mutable.

D The program will compile and run normally.

Rust's compiler prevents changing immutable variables by giving a compile-time error.

Which of these is the correct way to declare an immutable variable with value 10 in Rust?

A let mut x = 10;

B const x = 10;

C var x = 10;

D let x = 10;

By default, let declares an immutable variable.

Why does Rust prefer immutable variables by default?

A To make code run faster.

B To prevent accidental changes and bugs.

C Because mutable variables are not allowed.

D To save memory space.

Immutable variables help avoid bugs by preventing unintended changes.

What keyword is NOT used to declare variables in Rust?

A var

B mut

C let

D const

Rust does not use var; it uses let and const.

Explain what immutable variables are in Rust and how they affect your code.

Think about why Rust wants you to avoid changing variables unless you say so.

Describe how to declare a mutable variable in Rust and why you might want to do that.

Remember, mut means you can change the variable later.