Lesson video

Hello, everybody, welcome to computing.

It's Mrs. Franzsen here.

It's really great to see you.

I'm so glad that you've chosen my lesson today.

In this lesson, we are going to be looking at some coding.

Are you ready? Then let's get started.

By the end of this lesson, you will be able to fix the bugs that you can find in a programme.

Let's look at our keywords for today.

Our first keyword is the word, bug.

Can you see my image of a bug? In computing, a bug is an error or a mistake in code that stops it working properly or as expected.

And debug is our other keyword.

Debugging is the process of finding and correcting bugs in code.

In the first part of the lesson, we are going to look at describing how to debug a programme.

Have you ever made a programme and found out that it doesn't work in the way that you would like? Laura says, "My programme was meant to make the sprite change costume, but it isn't doing what I had planned." Oh, no, I wonder if you've ever had that experience when you've been programming.

Laura says, "My code is not working as I want it to!" Sofia says, "It may have a bug." The bug was one of our keywords, do you remember that? A bug is an error or a mistake in code that stops it from working properly or as expected.

The process of finding and correcting bugs in code is called debugging.

Every programmer will need to correct errors and debug their code.

Okay, it's time for a check now.

Let's have a look at this statement.

We start off with a blank.

Blank is the process of finding and correcting errors in code.

These errors are often called blank.

Okay, so we've just talked about these two keywords.

I want you to pause the video here and see if you can fill in the blanks.

Welcome back, well done for working on that question.

Let's have a look at our statement.

So our first blank here is debugging.

Debugging is the process of finding and correcting errors in code.

These errors are often called bugs.

Well done if you got that right.

Here are the five steps for debugging: Now, these are important, so make sure you listen carefully to the five steps.

Number one, review the task, what should the project do? Number two, test the project, see what goes wrong.

Number three, identify the bug.

Number four, fix the bug.

Number five, test the bug fix.

Does the code now do what it should? Aisha has noticed a problem in her programme.

The first step is to review the task.

What should the project do? Aisha says, "This is a drawing programme.

When I press the arrow keys, my sprite is supposed to move around." The next step is to test the project.

Aisha says, "I have tested my code, the pen down and erase commands work.

Some of the directions are fine, but the sprite is moving right instead of left." Oh no, that does sound like a bug.

Step three is to identify the bug.

Aisha says, "This is what should happen when the left arrow key is pressed: the sprite should point to the left and move 10 steps." This is Aisha's code on the right.

You can see she's got: when, left arrow, key pressed, point in direction 90, move 10 steps.

I wonder if you've noticed a bug yet.

Can you spot the bug? You can pause the video here to have a think about the bug and if you could spot it.

It is a tricky one to spot.

Aisha says, "The bug is in the point in direction block! It has the wrong value." Can you see it here from the diagram that the 90 value in the point in direction is not going to make her sprite go to the left? It's going to make it go to the right instead.

Step four is to fix the bug.

Aisha says, "To make the sprite point to the left, the value needs to be -90." The final step is to test the bug fix.

Does the code now do what it should? Aisha says, "My programme is working! I fixed the bug." And you can see that she's changed the value of the point in direction to be a -90.

True or false? Only new programmers will have bugs in their programmes.

Pause the video to think about your answer.

The answer was false.

Why? The answer was false, because every programmer will need to correct errors and debug their code.

Well done if you got that one right.

Okay, it's time to do a task now.

Here are the five steps for debugging, but they are in the wrong order.

I want you to think back to Aisha's problem with her programme, and then I want you to arrange the steps in the correct order.

So these steps are all in the wrong order, I'm going to read what's here.

It says: identify the bug.

Test the bug fix, does the code now do what it should? Fix the bug.

Test the project, see what goes wrong.

Review the task, what should the project do? I want you to pause the video here, go and unscramble my five steps for debugging so they're in the right order, and then come back and we can look at them together.

Welcome back, well done for all of your hard work in that task.

Here are the five steps for debugging in the correct order.

Number one, review the task, what should the project do? Number two, test the project, see what goes wrong.

Number three, identify the bug.

Number four, fix the bug.

And number five, test the bug fix, does the code now do what it should? In the second part of the lesson, we are going to find and fix bugs.

When you find a bug in your Scratch project, there are different ways that you can fix the error.

You could add a block.

You could change a block.

You could remove a block.

Time for a check now.

True or false? If a sprite is not moving, the best first step is to immediately start changing your code.

Pause the video here to have a think about that.

The answer is false.

Why? Remember the debugging steps: Always review the task, test the project, and identify the bug before trying to fix it.

If a sequence of code is not doing what it should be doing, you might need to add a block.

This code sequence should make the sprite move down when the arrow key is pressed.

What is missing? An event block is missing.

There is nothing to trigger the actions.

Add an event block and this code has been debugged.

You fixed the error.

If a sequence of code is not doing what it should be doing, you might need to change a value on a block.

This code sequence should make the sprite move down when the arrow key is pressed.

What needs to be changed? The value in the point in direction block is incorrect.

It should be changed to 180.

Change the value and this code has been debugged.

You fixed the error, just like that.

If a sequence of code is not doing what it should be doing, you might need to remove a block.

This code sequence should make the sprite move down from its current location.

What should be removed? The, go to x y, block should not be in this code sequence.

Remove the block and this code has been debugged.

You fixed the error.

Let's do a check here.

When debugging, what is the best way to check if a fix has worked? Is it A, test the fix by running the programme? B, make lots of changes at once and see what happens? C, delete the code and start again? Pause the video here to think about your answer.

Welcome back, well done for thinking about that question.

The answer is A, test the fix by running the programme.

Okay, it's time for a task now.

We are going to be doing some debugging today.

I want you to open the project.

The project is called fix-drawing.

The first part says there is a bug in the green flag code.

This is what should happen: When the green flag is clicked, the pencil should move to the centre, the pen colour should be set to blue, and all lines should be erased.

Test the programme, find the bug, and fix it.

You can see here I've got the coding blocks.

When the green flag is clicked, go to xy, and set pen colour to blue.

You can pause the video here to go and work on this part of the task, and then come back to see the answer.

Welcome back.

For number one, the green flag code.

The bug was: The lines were not erasing.

The fix is: Add an erase all block to the bottom of the green flag code.

Well done if you got that one right.

Let's look at the next one together.

Number two says, there is a bug in the move-up code.

This is what should happen: When the up arrow key is pressed, the sprite should point upwards and move 10 steps.

Test the programme, find the bug, and fix it.

You can see I've got the coding blocks here.

When the up arrow is pressed, point in direction 0.

You can pause the video here, go and work on finding and fixing that bug, and then come back to look at the answer.

Let's look at the answer for number two, the move-up code.

The bug was: The sprite doesn't move.

The fix is: Add the move 10 steps block.

Well done if you found that bug and fixed it.

Let's look at the next one together, number three.

There is a bug in the pen up code.

This is what should happen: When the u key is pressed, the pen should stop drawing when the sprite moves.

Test the programme, find the bug, and fix it.

You can see the coding blocks I used here.

I've got the event.

When the u key is pressed and I've got pen down.

Off you go, go and find that bug and fix it, and come back to look at the answer.

Welcome back.

Let's look at the pen up code.

The bug was: The sprite keeps drawing.

The fix is: Remove the pen down block and add the pen up block instead.

Well done if you got that one right.

Number four, there is a bug in the pen thickness code.

This is what should happen: When the 2 key is pressed, the pen line should get thinner.

Test the programme, find the bug, and fix it.

My coding block here, is when the 2 key is pressed, change pen size by 1.

Off you go and find the bug and fix it.

I'll be here when you get back to look at the answer.

This is the answer for number four, the pen thickness code.

The bug was: The pen line keeps getting thicker.

The fix is: To change the value of the, change pen size by, to minus one.

because that minus shows that it makes the line smaller.

Well done for all of your hard work on that task.

There were some tricky bugs there.

You worked really hard in this lesson today.

Let's summarise our learning.

Sometimes, if a programme doesn't work the way that you want it to, it's because of a bug.

A bug is a mistake in the code that stops it from working properly.

When this happens, you need to debug the programme.

Debugging means finding and fixing the error so that the programme works correctly.

There are different ways to fix a bug.

You might need to add a block, change a block, or remove a block to make sure the code works properly.

Testing the fix helps make sure the problem is solved.

Thank you for joining me in this lesson today.

I really enjoyed learning with you, and I hope to see you again soon.