Using if as expression in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean that if can be used as an expression in Rust?

In Rust, if can return a value, so you can assign the result of an if block to a variable. This means if is not just for control flow but also produces a value.

beginner

How do you assign a value to a variable using if as an expression?

You write <code>let variable = if condition { value1 } else { value2 };</code>. The variable gets the value from the block that matches the condition.

intermediate

What happens if you omit the else block when using if as an expression?

Rust requires an else block when using if as an expression to ensure both branches return a value. Omitting else causes a compile error.

intermediate

Can the blocks inside if expression return different types?

No. Both if and else blocks must return the same type because the variable assigned expects a single type.

beginner

Example: What is the value of <code>result</code> after this code?<br><pre>let number = 7;
let result = if number % 2 == 0 { "even" } else { "odd" };</pre>

The value of result is "odd" because 7 is not divisible by 2, so the else block runs.

What must you always include when using if as an expression in Rust?

A A loop inside the <code>if</code>

B A semicolon after <code>if</code>

C A return statement

D An <code>else</code> block

When using if as an expression, Rust requires an else block to provide a value for all cases.

What type must the if and else blocks return when used as an expression?

A They must return integers

B They can return any types

C They must return the same type

D They must return booleans

Both blocks must return the same type because the expression's value must have a single consistent type.

What is the value of x after this code?<br>

let x = if true { 10 } else { 20 };

A 10

B 20

C true

D Compile error

Since the condition is true, the if block runs and x is assigned 10.

Can you use if as an expression without assigning its value to a variable?

A Yes, but it’s uncommon

B No, it must always be assigned

C Yes, <code>if</code> can be used as a statement only

D No, <code>if</code> is only an expression

You can use if as an expression without assignment, but usually it’s used to produce a value for a variable.

What happens if the if block returns an integer and the else block returns a string?

A Rust converts the string to integer

B Rust throws a compile-time error

C The program runs but with warnings

D The <code>else</code> block is ignored

Rust requires both blocks to return the same type; otherwise, it causes a compile-time error.

Explain how if can be used as an expression in Rust and why it is useful.

Think about how you can choose a value based on a condition.

Describe what happens if you forget the else block when using if as an expression.

Rust wants to be sure what value to assign in all cases.