BBP Lesson 10: Loops

Definition: A loop is a set of instructions that are repeated. Also known as iteration.

:dart: Learning Objectives

By the end of this lesson, you will be able to:

• Understand what loops are and why they're powerful
• Create While loops that repeat based on conditions
• Build For loops to repeat a specific number of times
• Loop through lists to process each item
• Use break statements to exit loops when needed
• Connect loop blocks to real Python code

Let's Get Started! :rocket:

Understanding Loops

Imagine you're teaching a robot to do jumping jacks. Would you want to tell it "jump, jump, jump..." 50 times? Of course not! That's where loops come in - they're like a magic spell that makes the computer repeat instructions for you! :emoji:

Why Use Loops?

• Save time and effort: Instead of copy-pasting the same code over and over, write it once and let the loop do the work!
• Make interactive programs: Keep asking for input until the user gives the right answer
• Create patterns: Make Turtle draw amazing shapes by repeating movement steps
• Process lists: Go through each item in a list automatically

:information_source: Remember! Loops are one of the most powerful tools in programming. They turn repetitive tasks into simple, elegant code!

Getting Started with Loop Blocks

To access loop blocks in EduBlocks:

1. Click on the Loops category in the sidebar
2. You'll see different types of loop blocks available
3. Drag the loop block you need into your workspace

While Loops

Think of a While loop like a bouncer at a club - it keeps checking a condition and only lets the code inside run if the condition is True! :emoji:

How While Loops Work

A While loop keeps repeating as long as its condition remains True. It's perfect for:

• Waiting for user input
• Running a game until the player wins or loses
• Repeating actions until a specific goal is reached

:bulb: Pro Tip!

Be careful with While loops! If the condition never becomes False, your loop will run forever (called an "infinite loop"). Always make sure there's a way for the loop to end!

Creating Your First While Loop

Just like the if, elif or else blocks, a While loop will only run the commands inside it if the condition is True.

Steps to create a While loop:

1. Drag the while block from the Loops category
2. Add your condition (what to check)
3. Place the commands you want to repeat inside the loop
4. Make sure something in the loop can eventually make the condition False!

Input	Output

Real Python Connection :emoji:

In text-based Python, a While loop looks like this:

while condition:
    # Code to repeat goes here

The blocks make it visual, but it's the same concept!

For Loops

While loops are great when you don't know how many times to repeat, but what if you want to repeat exactly 10 times? That's where For loops shine! ⭐

Understanding For Loops

For loops are perfect when you:

• Know exactly how many times to repeat
• Want to count while looping
• Need to go through each item in a list

Your First For Loop

Let's create a For loop that repeats 5 times:

Steps to create a For loop:

1. Drag the for block from the Loops category
2. Set the variable name (usually i for "index")
3. Set the range (how many times to repeat)
4. Add the commands you want to repeat inside

Input	Output

:information_source: Remember! In a For loop with range 5:

• It repeats exactly 5 times
• The variable i starts at 0 (not 1!)
• Each time through, i increases: 0, 1, 2, 3, 4

The Loop Counter Variable

The i variable is special - it's the current index number of the loop:

• First loop: i = 0
• Second loop: i = 1
• Third loop: i = 2
• And so on...

:bulb: Pro Tip!

You don't have to use the i variable in your code! It's there to help the computer count, but you can ignore it if you just want to repeat something.

Input	Output

In this example, the i variable isn't used inside the loop, but it's still needed for the computer to track how many times it has repeated.

Real Python Connection :emoji:

In text-based Python, a For loop looks like this:

for i in range(5):
    # Code to repeat goes here

Looping Through Lists

One of the coolest things about For loops is that they can go through each item in a list automatically! It's like having a robot assistant that checks every item in your backpack one by one. :emoji:

How List Loops Work

A For loop can loop through items in a list, processing each one in order.

Understanding the parts:

• The x represents the current item being processed
• The y should be a list variable containing your items

Creating a List Loop

Steps to loop through a list:

1. Create a list variable with items
2. Drag the for x in y block from the Loops category
3. Replace x with a meaningful variable name (like "item" or "fruit")
4. Replace y with your list variable name
5. Add commands inside to process each item

Input	Output

:information_source: Remember! The loop goes through the list in order - first item first, last item last. The variable x (or whatever you name it) holds the current item being processed.

:bulb: Pro Tip!

Choose meaningful variable names! Instead of x, use names like:

• fruit for a list of fruits
• number for a list of numbers
• player for a list of player names

Breaking Out of Loops

Sometimes you need an emergency exit from a loop - that's where the break block comes in! It's like having an escape button when you've found what you're looking for. :emoji:

Understanding the Break Block

The break block immediately stops a loop and exits to the code after the loop.

When to Use Break

Break is useful when:

• You've found what you're searching for in a list
• The user wants to quit early
• A special condition is met
• You want to prevent unnecessary iterations

Using Break in Your Code

Steps to use the break block:

1. Place your loop (While or For)
2. Add conditional blocks (if/elif/else) inside the loop
3. Drag the break block inside the conditional
4. The loop will stop when that condition is met

Input	Output

:information_source: Remember! You can place the break block anywhere inside a loop - in While loops, For loops, or even nested loops! When break runs, it only exits the innermost loop it's in.

:bulb: Troubleshooting Tip!

If your loop isn't breaking when expected:

1. Check that your condition is correct
2. Make sure the break is inside the conditional block
3. Add print statements to see what's happening
4. Remember that break only exits one loop level

Real Python Connection :emoji:

In text-based Python, break works exactly the same way:

for item in my_list:
    if item == "stop":
        break
    print(item)

:tada: Optional Challenges

Ready to level up your loop skills? Try these challenges:

Challenge One: Password Checker

Create a While loop that keeps asking for a password until the user enters the correct one. Use break when they get it right!

Challenge 2: Number Counter

Make a For loop that counts from 1 to 100, but skips all numbers divisible by 7.

Challenge 3: List Explorer

Create a list of your favorite games. Use a For loop to print each one, but stop (break) if you find "Minecraft" in the list.

Challenge 4: Pattern Maker

Use nested loops (a loop inside another loop) to create interesting patterns with print statements or Turtle graphics!

You're Doing Great! :star2:

Congratulations! You've mastered loops - one of the most powerful concepts in programming! You can now:

• :white_check_mark: Create While loops for conditional repetition
• :white_check_mark: Build For loops for counted repetition
• :white_check_mark: Loop through lists to process data
• :white_check_mark: Use break to exit loops when needed

Loops are everywhere in programming - from games that run until you quit, to apps that process your photos one by one. You're now ready to create more complex and interesting programs!

Keep practicing with loops - they're the key to making your programs do amazing things without writing tons of repetitive code! :rocket: