If–else expression in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an if–else expression in Rust?

An if–else expression in Rust lets you choose between two paths based on a condition. It evaluates to a value, so you can assign its result to a variable.

beginner

How do you write a simple if–else expression in Rust?

You write it like this:<br><pre>let x = if condition { value1 } else { value2 };</pre><br>The variable x gets value1 if the condition is true, otherwise value2.

intermediate

Can if–else expressions in Rust return different types?

No. Both branches of an if–else expression must return the same type because Rust needs to know the exact type of the expression's result.

intermediate

What happens if you omit the else branch in an if expression?

If you omit else, the if expression returns () (unit type) when the condition is false. This can cause type mismatch if you try to assign it to a variable expecting another type.

beginner

Why is if–else called an expression in Rust, not just a statement?

Because it produces a value that can be used in assignments or other expressions. This makes Rust code concise and expressive.

What does this Rust code do?<br>

let x = if 5 > 3 { 10 } else { 20 };

A Assigns 5 to x

B Assigns 20 to x because 5 > 3 is false

C Causes a compile error

D Assigns 10 to x because 5 > 3 is true

Since 5 is greater than 3, the condition is true, so x gets 10.

In Rust, what type must both branches of an if–else expression return?

A They can return any types

B They must return the same type

C One branch returns a type, the other returns unit

D They must return integers

Both branches must return the same type so Rust knows the expression's type.

What is the value of this expression if the condition is false?<br>

if false { 1 } else { 2 }

A 2

B 1

C ()

D Compile error

The else branch runs when the condition is false, so the value is 2.

What happens if you write:<br>

let x = if true { 5 };

?

A Compile error because else is missing

B x is ()

C x is uninitialized

D x is 5

Rust requires else branch for if used as an expression to ensure both branches return a value.

Why is if–else useful as an expression in Rust?

A Because it is faster than other languages

B Because it can only run statements

C Because it returns a value that can be assigned

D Because it does not need braces

If–else expressions return values, allowing concise and clear code.

Explain how an if–else expression works in Rust and why both branches must return the same type.

Think about how Rust needs to know the type of the whole expression.

Describe what happens if you use an if expression without an else branch when assigning to a variable.

Consider what Rust returns when the condition is false and no else is given.