Expressions and statements

Learn the difference between expressions and statements.

Expressions and statements

In Rust a statement does something but produces no value (let x = 5;); an expression produces a value (5 + 1, kare(3), if ..., { ... }). Putting a semicolon after an expression turns it into a statement.

let y = {
    let x = 3;
    x + 1        // the block's value: 4
};
println!("{y}");

That's why let x = (let y = 6); is invalid: let doesn't produce a value.

match is an expression too

To classify a value and assign the result directly to a variable, a match expression is used:

let puan = 72;
let harf = match puan {
    90..=100 => 'A',
    70..=89 => 'B',
    50..=69 => 'C',
    _ => 'F',
};
println!("{harf}");   // B

Every arm must return the same type; otherwise the compiler reports an error.

Exercise Letter grade

Write the fn harf(puan: u32) -> char function with a match expression: 90–100 'A', 70–89 'B', 50–69 'C', otherwise 'F'. Print harf(95), harf(72) and harf(30) on one line.

Show example solution

fn harf(puan: u32) -> char {
    match puan {
        90..=100 => 'A',
        70..=89 => 'B',
        50..=69 => 'C',
        _ => 'F',
    }
}

fn main() {
    println!("{} {} {}", harf(95), harf(72), harf(30));
}

Test yourself

Which of these is an expression?
- fn f() {}
- use std::io;
- { let a = 2; a * a }
- let a = 2;
Show answer

{ let a = 2; a * a } — The block produces the value of its last expression (4); the others are declarations and statements that produce no value.

if as an expression

let durum = ____ yas >= 18 { "yetişkin" } else { "çocuk" };

Show answer

let durum = if yas >= 18 { "yetişkin" } else { "çocuk" };

Code and kind

let x = 5;

Statement
5 + 1

Expression
{ x + 1 }

A value-producing block
x + 1;

A statement discarding the value

Next lesson: Early return

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