if/else Expressions

Basic if/else

An if expression evaluates a boolean condition and runs the associated block only when it is true; an optional else block runs otherwise. No parentheses are needed around the condition, unlike C or Java.

Example: Basic if/else

fn main() {
    let number = 7;
    if number > 5 {
        println!("Greater than five");
    } else {
        println!("Five or less");
    }
}

else if Chains

Multiple conditions can be chained with else if, checked in order from top to bottom. The first matching branch runs, and the rest are skipped.

Example: else if Chains

fn main() {
    let grade = 85;
    if grade >= 90 {
        println!("A");
    } else if grade >= 80 {
        println!("B");
    } else {
        println!("C or below");
    }
}

if as an Expression

Because if is an expression, not just a statement, it can produce a value directly, which you can assign to a variable. Both branches must return values of the same type.

Note: Notice there are no semicolons after 5 and 6 -- they are the tail expressions of each block.

Example: if as an Expression

fn main() {
    let condition = true;
    let number = if condition { 5 } else { 6 };
    println!("number is {}", number);
}

Condition Must Be a Bool

Rust requires the if condition to be an actual bool value; it will not implicitly treat a nonzero integer as true, unlike C. This prevents an entire category of bugs from mistyped conditions.

Example: Condition Must Be a Bool

fn main() {
    let count = 3;
    if count != 0 {
        println!("count is non-zero: {}", count);
    }
}