What is the difference between iter map and for loop

The for loop iterates over a collection by calling next() on an iterator, while .map() transforms each item in an iterator into a new value without executing the transformation until the iterator is consumed. Use for when you need to perform side effects like printing or modifying state, and use .map() when you want to create a new collection of transformed data.

let numbers = vec![1, 2, 3];

// for loop: executes immediately for side effects
for n in &numbers {
    println!("Got: {}", n);
}

// .map(): creates a new iterator of transformed values
let doubled: Vec<i32> = numbers.iter().map(|n| n * 2).collect();

A for loop is like walking down a line of people and talking to each one individually to do something right now. .map() is like handing out a form to everyone in line to fill out, collecting the finished forms later to create a new list. You use for when you need to act immediately, and .map() when you want to transform data into a new set.