Conditionals

Rust's if works like every other language's at first glance, but with one real difference: if is an expression, not a statement, so it can produce a value directly — which is also why Rust has no separate ternary operator.

if / else if / else

Rust src/main.rs

fn main() {
    let temp = 15;

    if temp > 30 {
        println!("Hot");
    } else if temp > 15 {
        println!("Mild");
    } else {
        println!("Cold");
    }
}

Output

Cold

No parentheses are needed around the condition (unlike C or Java), but the curly braces are never optional — there's no single-statement-without-braces shorthand.

if as an expression

Because if produces a value, you can assign its result directly to a variable instead of declaring the variable first and reassigning it in each branch:

Rust src/main.rs

fn main() {
    let age = 20;
    let category = if age >= 18 { "adult" } else { "minor" };
    println!("{}", category);
}

Output

adult

Both branches produce values of the same type here (&str) — that's not a style choice, it's required. An if used as an expression must have every branch evaluate to the exact same type, and it must have an else, since the compiler needs to know what value comes out no matter which branch runs.

Rust src/main.rs — this won't compile

let category = if age >= 18 { "adult" } else { 0 };

Compiler output

error[E0308]: `if` and `else` have incompatible types
  |
  |     let category = if age >= 18 adult else 0;
  |                                    -------          ^ expected `&str`, found integer
  |                                    |
  |                                    expected because of this

Note: this is also why Rust has no ? : ternary operator — if as an expression already covers that use case, and reads more clearly once you're used to it. For matching against several specific values rather than a single condition, the match expression (covered in the Enums & Pattern Matching lesson) is usually the better tool.

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