Is there a way to know how many iterations we have done in a for loop?

Question

Is there an easy way to know how many iteration we have done in a for loop?

If I have this code

for line in lines {
    println!("{}: {}", linenumber, line);
}

How can I easily get the number linenumber? Am I required to use an external counter variable?

Answer 1

It should be as simple as:

for (linenumber, line) in lines.enumerate() {
    println!("{}: {}", linenumber, line);
}

You can also do

#[macro_use]
extern crate itertools;

fn main() {
    for (linenumber, line) in izip!(0.., lines) {
        println!("{}, {}", linenumber, line);
    }
}

for more flexibility. This has the advantage of letting you change things like the start and step of the numbering as well as the number of zipped elements.