What is the difference between usize and u32 in Rust? When to use which?

Hello everyone! I started learning Rust a couple of weeks ago and encountered something I don't understand. In The Rust Programming Language book, I often see the `usize` type used for indices and lengths, but I also encounter `u32`. I can't figure out the fundamental difference between them. For example, I wrote a simple program that iterates over vector elements: ```rust fn main() { let v = vec![10, 20, 30, 40, 50]; // Option 1: using u32 for i in 0..v.len() as u32 { println!("{}", v[i as usize]); } // Option 2: using usize for i in 0..v.len() { println!("{}", v[i]); } } ``` The first option works, but I have to do a lot of type casting: `as u32` and `as usize`. The second option works without any casting. But I've heard that