Loop and exit
- Rust course
- Beginner
- Lesson 29/115
- 6 min
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}"); // 243continue skips the rest of the iteration; for example, to skip empty lines.
Practice 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.
Starter code
fn main() {
// buraya yaz
}Sample 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");
}Expected output
işlendi: 5 + 1 güle güle
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 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 Correct answer
- Nothing
- The program crashes
Explanation: read_line appends to the existing String; without clearing it accumulates like "12 * 3\n5 + 1\n".
2 Leave the loop
if satir == "çık" {
____;
}if satir == "çık" {
break;
}Explanation: break ends the nearest loop.
3 Statement and effect
| Term | Meaning |
|---|---|
loop |
Infinite loop |
break |
Ends the loop |
break n |
Returns a value |
continue |
Moves to the next iteration |