while loop
- Rust course
- Beginner
- Lesson 39/115
- 4 min
Loop while a condition holds with while.
The while loop
while repeats as long as the condition is true; the condition is checked at the start of every iteration:
let mut geri = 3;
while geri > 0 {
println!("{geri}...");
geri -= 1;
}
println!("kalkış!");To walk a collection by index, for is preferred over while; it removes the risk of index mistakes and the cost of bounds checks.
Counting digits
while is natural for work whose number of iterations isn't known in advance. For example, summing a number's digits:
let mut n = 4096;
let mut toplam = 0;
while n > 0 {
toplam += n % 10;
n /= 10;
}
println!("{toplam}"); // 19Practice Digit count
Write fn basamak(mut n: u64) -> u32: compute the digit count by dividing the number by 10 in a while n >= 10 loop (1 for 0). Print basamak(0), basamak(7) and basamak(123456) on one line.
Starter code
fn main() {
// buraya yaz
}Sample solution
fn basamak(mut n: u64) -> u32 {
let mut sayi = 1;
while n >= 10 {
n /= 10;
sayi += 1;
}
sayi
}
fn main() {
println!("{} {} {}", basamak(0), basamak(7), basamak(123456));
}Expected output
1 1 6
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the difference between <code>while</code> and <code>loop</code>?
- There is no difference
- loop is slower
- while checks a condition at the start of each iteration; loop repeats unconditionally Correct answer
- while returns a value
Explanation: Returning a value with break exists only for loop; while always produces ().
2 Conditional loop
____ n > 1 {
n /= 2;
adim += 1;
}while n > 1 {
n /= 2;
adim += 1;
}Explanation: while repeats the body as long as the condition is true.
3 Loop and use
| Term | Meaning |
|---|---|
loop |
Unconditional, with break |
while |
While a condition holds |
for |
Iterating a collection / range |
n /= 10 |
Drops the last digit |