for Loops

The for`forloop is used to loop a particular number of times. Rust’s` loop is used to loop a particular number of times. Rust’s for`forloops work a bit differently than in other systems languages, however. Rust’s` loops work a bit differently than in other systems languages, however. Rust’s for`forloop doesn’t look like this “C-style”` loop doesn’t look like this “C-style” for`for` loop:

for (x = 0; x < 10; x++) {
    printf( "%d\n", x );
}

Instead, it looks like this:

fn main() { for x in 0..10 { println!("{}", x); // x: i32 } }
for x in 0..10 {
    println!("{}", x); // x: i32
}

In slightly more abstract terms,

fn main() { for var in expression { code } }
for var in expression {
    code
}

The expression is an iterator. The iterator gives back a series of elements. Each element is one iteration of the loop. That value is then bound to the name var`var, which is valid for the loop body. Once the body is over, the next value is fetched from the iterator, and we loop another time. When there are no more values, the`, which is valid for the loop body. Once the body is over, the next value is fetched from the iterator, and we loop another time. When there are no more values, the for`for` loop is over.

In our example, 0..10`0..10is an expression that takes a start and an end position, and gives an iterator over those values. The upper bound is exclusive, though, so our loop will print` is an expression that takes a start and an end position, and gives an iterator over those values. The upper bound is exclusive, though, so our loop will print 0`0through` through 9`9, not`, not 10`10`.

Rust does not have the “C-style” for`for` loop on purpose. Manually controlling each element of the loop is complicated and error prone, even for experienced C developers.