Loop labels in Rust - Mini Project: Build & Apply

Loop Labels in Rust

📖 Scenario: Imagine you are organizing a treasure hunt game. You have several boxes, and each box contains several smaller boxes. You want to find a special item inside these nested boxes. To do this, you need to check each smaller box inside each big box. Sometimes, when you find the item, you want to stop searching immediately, even if you are inside a nested loop.

🎯 Goal: You will write a Rust program that uses loop labels to break out of nested loops when a special item is found.

📋 What You'll Learn

Create a nested loop structure with two loops: an outer loop labeled 'outer and an inner loop labeled 'inner.

Use break 'outer to exit both loops when a condition is met.

Print messages to show the progress of the search and when the item is found.

💡 Why This Matters

🌍 Real World

Loop labels help when you have nested tasks and want to stop or skip outer tasks from inside inner tasks, like searching in nested boxes or menus.

💼 Career

Understanding loop labels is useful for writing clear and efficient Rust code, especially in systems programming, game development, and complex data processing.

1

Create nested loops with labels

Write a nested loop structure in Rust with an outer loop labeled 'outer and an inner loop labeled 'inner. Inside the inner loop, print "Checking smaller box". Inside the outer loop, print "Checking big box" before the inner loop starts.

Rust

# Create an outer loop labeled 'outer'
# Inside it, print "Checking big box"
# Create an inner loop labeled 'inner'
# Inside it, print "Checking smaller box"

Need a hint?

Use 'outer: loop { ... } to label the outer loop and 'inner: loop { ... } for the inner loop. Use println! to print messages.

2

Add a counter to track smaller boxes

Create a variable called smaller_box_count and set it to 0 before the outer loop. Inside the inner loop, increase smaller_box_count by 1 each time you check a smaller box.

Rust

'outer: loop {
    println!("Checking big box");
    'inner: loop {
        println!("Checking smaller box");
        // Increase smaller_box_count here
        break 'inner;
    }
    break 'outer;
}

Need a hint?

Declare smaller_box_count as mutable with let mut. Increase it inside the inner loop.

3

Use loop labels to break out when item is found

Inside the inner loop, add an if statement that checks if smaller_box_count equals 3. If true, print "Item found!" and use break 'outer to stop both loops.

Rust

let mut smaller_box_count = 0;
'outer: loop {
    println!("Checking big box");
    'inner: loop {
        println!("Checking smaller box");
        smaller_box_count += 1;
        // If smaller_box_count is 3, print "Item found!" and break 'outer
        break 'inner;
    }
    break 'outer;
}

Need a hint?

Use if smaller_box_count == 3 to check the count. Use break 'outer to exit both loops.

4

Print the total smaller boxes checked

After the loops, print "Total smaller boxes checked: {smaller_box_count}" using an f-string style with println!.

Rust

let mut smaller_box_count = 0;
'outer: loop {
    println!("Checking big box");
    'inner: loop {
        println!("Checking smaller box");
        smaller_box_count += 1;
        if smaller_box_count == 3 {
            println!("Item found!");
            break 'outer;
        }
        break 'inner;
    }
}
// Print total smaller boxes checked here

Need a hint?

Use println!("Total smaller boxes checked: {}", smaller_box_count); to show the final count.