Loop and exit

Keep calculating with loop, break and a quit command.

Loop and exit

The calculator must keep running until the user types çık. loop is an infinite loop left with break. On every iteration the buffer is cleared with clear:

let mut girdi = String::new();
loop {
    girdi.clear();
    if io::stdin().read_line(&mut girdi).unwrap() == 0 {
        break;              // EOF (Ctrl+D)
    }
    let satir = girdi.trim();
    if satir == "çık" {
        break;
    }
    match isle(satir) { /* ... */ }
}

loop is an expression

break can also return a value, so loop can be used as an expression:

let mut n = 1;
let ilk_buyuk = loop {
    n *= 3;
    if n > 100 {
        break n;
    }
};
println!("{ilk_buyuk}");  // 243

continue skips the rest of the iteration; for example, to skip empty lines.

Exercise Command loop

Try the loop with an array instead of stdin: process the commands ["5 + 1", "", "çık", "9 * 9"] in order; continue on an empty line, break on "çık", otherwise print the line as işlendi: .... Print güle güle at the end.

Show example solution

fn main() {
    for komut in ["5 + 1", "", "çık", "9 * 9"] {
        if komut.is_empty() {
            continue;
        }
        if komut == "çık" {
            break;
        }
        println!("işlendi: {komut}");
    }
    println!("güle güle");
}

Test yourself

What happens if <code>girdi.clear()</code> isn't called in the loop?
- No input is read
- The new line is appended to the old one and parsing breaks
- Nothing
- The program crashes
Show answer

The new line is appended to the old one and parsing breaks — read_line appends to the existing String; without clearing it accumulates like "12 * 3\n5 + 1\n".

Leave the loop

if satir == "çık" {
    ____;
}

Show answer

if satir == "çık" {
    break;
}

Statement and effect

loop

Infinite loop
break

Ends the loop
break n

Returns a value
continue

Moves to the next iteration

Next lesson: Defining with fn

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies