Rust: from idea to program · Lesson 04 / 08

Repeat with a beginning and an end

The robot collects one, two and three parts at three stations. Instead of copying statements, we will traverse a sequence with for.

Let's discover together

1
for value in 1..4 visits 1, 2 and 3. The start is included; the end after .. is excluded. Each iteration runs the block once.
2
An accumulator starts with a value and is updated each iteration: let mut total = 0; and, inside the block, total += value;.
3
Trace the states: start at 0, add 1 to get 1; add 2 to get 3; add 3 to finish at 6. Writing these states helps explain the loop.
4
1..=4 includes 4 and makes four iterations. But 0..0 contains no values and makes zero iterations. A for loop ends when its sequence ends.

✦

YOUR MISSION

Predict how many iterations a loop makes, the total and what changes with an inclusive range.

Take it with you

Make a table for 2..5: current value and total after adding. Then predict 0..0 without executing it.

Show me the Rust behind it

This part is optional. You don't need to memorize the code to continue.

fn main() {
    let mut total = 0;
    for value in 1..4 {
        total += value;
    }
    println!("{total}");
}

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Repeat with a beginning and an end

Let's discover together

Now it's your turn

Trace the parts collection

Take it with you

My files and GitHub

Your file for this lesson

Save to my GitHub

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