Loops

Looping through data is pretty fundamental, so it shouldn't be a surprise that Rust supports loops.

For Loops

Take the following C code:

#include <stdio.h>

int main() {
    int i;
    for (i = 0; i < 10; i++) {
        printf("%d\n", i);
    }
    return 0;
}

Unsurprisingly: this prints 0 through 9.

Here's a Rust equivalent:

fn main() {
    for i in 0..10 {
        println!("{i}");
    }
}

The output is the same, but the syntax is quite different:

0..10 is an exclusive range. It provides an iterator over every number in the range, exclusing the last one. We'll worry about iterators later.
i only exists inside the loop scope. (In C++ and later C editions you can do for (int i=0; i<10; i++) for the same effect).
You don't have any control over the operation that occurs for each iteration. Rust just ticks through each entry in the range.

If you prefer an inclusive range:

fn main() {
    for i in 0 ..= 10 {
        println!("{i}");
    }
}

We'll look at for_each equivalency later.

This C should look familiar, too:

#include <stdio.h>

int main() {
    int i = 0;
    while (i < 10) {
        printf("%d\n", i);
        i += 1;
    }
    return 0;
}

Equivalent Rust code looks like this:

fn main() {
    let mut i = 0;
    while i < 10 {
        println!("{i}");
        i += 1;
    }
}

Sadly, Rust doesn't protect you from an infinite while loop either!

Rust adds one more type of loop, named loop. loop runs forever, or until a break statement is hit.

fn main() {
    let mut i = 0;
    loop {
        println!("{i}");
        i += 1;
        if i > 9 {
            break;
        }
    }
}