Rust if else

In Rust, if is not just a statement (like in many other programming languages) — it is also an expression.
This means it can return values, making Rust’s conditional logic both powerful and flexible.

In this tutorial, we’ll cover:

1. The basics of if
2. Using else if and else
3. Using if as an expression (returning a value)
4. Common mistakes to avoid

The Basics of Rust if-else Statement #

The simplest form of if checks whether a condition is true:

fn main() {
    let number = 7;

    if number < 10 {
        println!("The number is less than 10");
    }
}
Code language: Rust (rust)

• The condition (number < 10) must be a boolean value (true or false).
• Unlike some languages, Rust does not automatically convert numbers to booleans.

Valid:

if number < 10 { ... }
Code language: Rust (rust)

Invalid (will not compile):

if number { ... } // ERROR: expected `bool`, found integer
Code language: Rust (rust)

Using else if and else #

You can add multiple conditions with else if and a fallback with else:

fn main() {
    let number = 15;

    if number < 10 {
        println!("The number is less than 10");
    } else if number < 20 {
        println!("The number is between 10 and 19");
    } else {
        println!("The number is 20 or greater");
    }
}
Code language: Rust (rust)

• The first condition that is true will run.
• If none are true, the else block runs.
• Only one branch is executed.

Using if as an Expression #

Here’s where Rust is special: if can return values.

fn main() {
    let number = 3;

    let result = if number % 2 == 0 {
        "even"
    } else {
        "odd"
    };

    println!("The number is {}", result);
}
Code language: Rust (rust)

• if and else blocks must return the same type.
• Both branches return a string slice (&str in this example).

This code will not compile:

let result = if number % 2 == 0 {
    5
} else {
    "odd"  // ERROR: mismatched types
};
Code language: Rust (rust)

Common Mistakes to Avoid #

Forgetting braces {}

In Rust, braces are always required around the block of code after if, else if, or else.

if number < 10 println!("Too small"); // ERRORCode language: Rust (rust)

Correct:

if number < 10 {
    println!("Too small");
}Code language: Rust (rust)

Mismatched types in expressions

Both branches of if must evaluate to the same type (or () if no value is returned).

Rust if-else Example: Grading System #

Let’s put everything together:

fn main() {
    let score = 85;

    let grade = if score >= 90 {
        "A"
    } else if score >= 80 {
        "B"
    } else if score >= 70 {
        "C"
    } else if score >= 60 {
        "D"
    } else {
        "F"
    };

    println!("Your grade is {}", grade);
}
Code language: Rust (rust)

Output:

Your grade is B

Summary #

• if checks conditions and requires a boolean.
• Use else if for multiple conditions and else as a fallback.
• if is an expression in Rust — it can return values.
• Both branches of an if expression must return the same type.
• Always use braces {} for clarity and safety.