if-else

Branch with if, else if and else.

if-else

An if condition needs no parentheses but must be a bool; Rust doesn't turn numbers into true/false on its own:

let sicaklik = 24;
if sicaklik > 30 {
    println!("sıcak");
} else if sicaklik > 15 {
    println!("ılık");
} else {
    println!("soğuk");
}

if n { ... } (n a number) is a compile error; write if n != 0.

if as an expression

An if expression is used to choose a value and bind it directly:

let yas = 16;
let bilet = if yas < 18 { 25 } else { 40 };
println!("{bilet} TL");

Complex conditions are combined with &&, || and !; thanks to short-circuiting, v.len() > 0 && v[0] == 1 doesn't panic on an empty vector.

Exercise Ticket price

Write fn bilet(yas: u32) -> u32: return 0 under 6, 25 under 18, and 40 otherwise (with an if/else if/else expression). Print bilet(4), bilet(12) and bilet(30) on one line.

Show example solution

fn bilet(yas: u32) -> u32 {
    if yas < 6 {
        0
    } else if yas < 18 {
        25
    } else {
        40
    }
}

fn main() {
    println!("{} {} {}", bilet(4), bilet(12), bilet(30));
}

Test yourself

Why doesn't <code>let x = if true { 1 } else { "bir" };</code> compile?
- It compiles
- The arms have different types (i32 and &str)
- true can't be a constant
- else is unnecessary
Show answer

The arms have different types (i32 and &str) — Because if is an expression it must have a single type; every arm must produce the same type.

Middle condition

if n > 0 {
    println!("pozitif");
} ____ n < 0 {
    println!("negatif");
}

Show answer

if n > 0 {
    println!("pozitif");
} else if n < 0 {
    println!("negatif");
}

Temperature and output

35

sıcak (hot)
24

ılık (mild)
5

soğuk (cold)
if n {}

Compile error

Next lesson: match basics

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