Hi,
as a little fun project I wrote this prime generator. It is not fully correct because I assume that 1 is not prime and 2 is prime.
fn main() {
let mut primes = Vec::new();
primes.push(2);
let mut found = false;
for n in 3..100 {
for prime in &primes {
if n % prime == 0 {
found = true;
break;
}
}
if found == false {
primes.push(n);
}
found = false;
}
println!("{:?}", primes);
}
Because it is a bit straight forward and I want to learn to write better Rust code maybe someone might help me to make this more idiomatic Rust. Don't be confused with the found variable. It means that I found a number that is NOT prime
fn primes(max: u32) -> Vec<u32> {
let mut primes = vec![2];
for n in 3..max {
if primes.iter().all(|p| n % p != 0) {primes.push(n);}
}
primes
}
fn main() {
println!("{:?}", primes(100));
}
What's incorrect about that assumption? In fact 1 is not prime and 2 is prime.
Don't mutate all over the place when all you need is to find whether there are divisors for a given number. Use the vec![] macro for creating a vector from a known set of elements.
fn main() {
let mut primes = vec![2];
for n in 3..100 {
if primes.iter().all(|&p| n % p != 0) {
primes.push(n);
}
}
println!("{:?}", primes);
}
This is pattern matching at work! The Book covers this topic in chapter 18.
The short version is that with the &p pattern, the p variable will be a copy of the number, just a simple u32. Without it, the type in the p variable will be &u32. And furthermore, because of Rust's Deref coercions, n % p still works in both cases, too!
