Welcome to the Sands of Until! Today, we’re going to learn about something called an “until” loop in coding. It’s a fun and useful tool that helps us repeat actions until a certain condition is met. Let’s dive in!
An “until” loop is a type of loop that keeps running until a specific condition is true. You start by using the keyword “until,” followed by the condition you want to meet. Below that, you can list any number of commands, but remember to indent them properly.
Here’s a simple example:
until near bridge
// commands
In this example, the condition is “near bridge.” This means the loop will keep executing the commands until you are near the bridge. Once you reach the bridge, the loop stops, and you move on to the next part of your code.
Let’s imagine a challenge where a mouse needs to grab a match and then go to a pile to drop it. We can use two “until” loops to solve this:
But watch out! Sometimes, you might accidentally create an endless loop. This happens if the mouse never turns toward the pile, causing it to keep moving without getting closer. To fix this, make sure the condition will eventually be met. For example, turn toward the pile before stepping.
Let’s look at another example using a function called “chase.” Here, the match is a moving target:
function chase(m)
until near m
// turn and step commands
In this function, “m” is a placeholder. The first time “chase” is called, “m” represents the match. The second time, it represents the pile. Since the match is moving, the mouse needs to keep turning toward it and stepping closer until it’s near enough to grab it. When it’s near the pile, it will drop the match.
And that’s how an “until” loop works! It’s your turn to try using “until” loops in your coding adventures. Good luck, and have fun!
Imagine you’re a character in a video game. Write a short story where you use an “until” loop to complete a quest. Describe the condition that needs to be met and the actions you take repeatedly until you achieve your goal. Share your story with the class!
Design a simple maze on paper and write pseudocode using “until” loops to navigate through it. Your goal is to reach the end of the maze. Exchange mazes with a classmate and try to solve each other’s using your pseudocode skills.
Use a coding platform like Scratch or Code.org to create a project where a character moves towards an object using an “until” loop. Experiment with different conditions and see how they affect the character’s movement. Present your project to the class and explain how the “until” loop works in your code.
Work in pairs to debug a piece of code that uses an “until” loop. One student writes a code snippet with a deliberate mistake that causes an endless loop. The other student must identify and fix the error. Discuss what went wrong and how you solved it.
Think of real-life situations where you perform actions repeatedly until a condition is met, like brushing your teeth until a timer goes off. Create a list of these scenarios and discuss how they relate to “until” loops in coding. Share your findings with the class.
Sure! Here’s a sanitized version of the transcript, removing any unnecessary filler words and maintaining clarity:
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[Music] Welcome to the Sands of Until. Let’s learn about “until.”
An “until” loop is a type of loop that runs until a specified condition is met. This is how you write an “until” loop: use the keyword “until,” followed by the condition you want to meet. You can include any number of commands below, but each must be indented.
Here’s an example:
“`
until near bridge
// commands
“`
In this case, the condition is “near bridge.” Essentially, I want to execute the commands until I’m near the bridge. As soon as I’m near the bridge, the loop will stop, and I’ll proceed to the next command outside of the loop.
Let’s look at an example with two “until” loops. In this challenge, we want the mouse to grab a match and then go to the pile to drop it.
The first “until” loop will have the mouse stepping until it’s near the match. After grabbing the match, the mouse will then loop and step until it’s near the pile, where it can drop the match.
Now, we have a situation where we encounter an endless loop. The mouse never turns toward the pile, so it will keep stepping without getting closer to it. This loop will run indefinitely.
To avoid this, we need to ensure that when we have an “until” loop, the condition will eventually be met. Before stepping, we should turn toward the pile and then step.
In this example, we could have placed the turn command above the “until near pile” condition, as the pile never moves. This means it didn’t have to be inside the loop; it could have been positioned right above the “until” and still worked.
Let’s look at another example that’s similar but involves a function called “chase.” In this case, the match is a moving target.
Within the function, we use “until near m,” where “m” is our parameter that represents the match the first time “chase” is called. The second time, “m” represents the pile.
In this loop, since the match is moving, we need to always turn toward it and step closer each time until we’re near it. Once we’re near, we’ll grab it, and in the case of the pile, we’ll drop it.
Let’s see how this works.
Oops! I made a mistake. Instead of saying “match,” I should just say “m.” The first time, it will be the match, and the second time, it will be the pile.
That’s it!
[Music] It’s your turn to use “until.” Good luck!
[Music]
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This version maintains the instructional content while removing unnecessary filler and clarifying the message.
Loop – A sequence of instructions that repeats until a certain condition is met. – Example sentence: In computer programming, a loop can help you repeat a task without writing the same code multiple times.
Until – Used to specify that something will happen up to a certain point or condition. – Example sentence: The program will keep adding numbers until the total reaches 100.
Condition – A statement or expression that controls the execution of code based on whether it is true or false. – Example sentence: The if statement checks the condition to decide which block of code to execute.
Commands – Instructions given to a computer to perform specific tasks. – Example sentence: The programmer typed several commands to compile and run the code.
Mouse – A device used to interact with a computer by pointing and clicking on objects on the screen. – Example sentence: You can use the mouse to drag and drop files into different folders on your computer.
Match – To find or identify items that are the same or similar. – Example sentence: The program uses an algorithm to match the user’s input with the correct answer.
Pile – A collection of items stacked or grouped together, often used metaphorically in coding to describe a stack of data or tasks. – Example sentence: The programmer had a pile of error messages to sort through before the code could run smoothly.
Endless – Without a limit or end, often used to describe a loop that continues indefinitely. – Example sentence: An endless loop can cause a program to freeze if there is no condition to stop it.
Function – A block of organized, reusable code that performs a single action or task. – Example sentence: The function calculates the sum of two numbers and returns the result.
Code – A set of instructions written in a programming language that a computer can execute. – Example sentence: Learning to write code is like learning a new language that allows you to communicate with computers.
