Computer Science
Grade 5
20 min
Debugging Event-Driven Programs
Learn how to identify and fix errors in event-driven programs.
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1
Introduction & Learning Objectives
Learning Objectives
Identify the event that is supposed to trigger an action in a program.
Trace the code inside an event handler block to predict its outcome.
Define what a 'bug' is in the context of an event-driven program.
Use a step-by-step process to find and fix a bug related to a specific event.
Explain why the order of code blocks inside an event handler matters.
Correct code that uses the wrong event trigger for a desired action.
Ever clicked a button in a game and... nothing happened? 🐛 That's a bug! Let's become bug detectives and learn how to fix our code when events don't work as planned.
In this lesson, you'll learn how to find and fix mistakes, called 'bugs,' in your event-driven programs. This skill, called debugging,...
2
Key Concepts & Vocabulary
TermDefinitionExample
EventAn action that a computer program can recognize, like a mouse click, a key press, or a sprite touching another sprite.In a game, pressing the up-arrow key is an event.
Event HandlerA block of code that is set up to run when a specific event happens.The `when up-arrow key pressed` block is an event handler. The code inside it will only run when you press the up-arrow key.
BugAn error or mistake in a computer program that causes it to behave in an unexpected or wrong way.You code a cat to say 'Meow!' when clicked, but instead it spins in a circle. The spinning is a bug.
DebuggingThe process of finding and fixing bugs in a program.You look at your code line-by-line to figure out why the cat is spinning instead of meowing. That's debugging!
Code Traci...
3
Core Syntax & Patterns
Rule 1: Match the Event to the Action
Event Trigger -> Event Handler -> Expected Action
Always check that the event you are using (like 'when this sprite clicked') is the correct one for the action you want to happen. If you want something to happen when you click a sprite, don't use the 'when green flag clicked' event handler.
Rule 2: Check the Conditions
Inside an Event Handler, check all `if-then` blocks.
Sometimes the event works, but the code inside doesn't run because a condition is not met. For example, an `if <touching color red?>` block won't run if your sprite is not touching the color red.
Rule 3: Follow the Order
Code inside an event handler runs from top to bottom.
The order of your code blocks matters. If y...
4 more steps in this tutorial
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Challenging
Two events happen at almost the same time. Event A sets a variable `X` to 10. Event B sets `X` to 20. After both events fire, you expect `X` to be 20, but sometimes it is 10. This type of bug is called a...
A.Syntax error
B.Race condition
C.Looping error
D.Costume error
Challenging
A bug in your game only happens after you perform a very specific sequence of actions: 1. Click the red button. 2. Wait 5 seconds. 3. Click the blue button. What is the BEST debugging strategy for this?
A.Restart the computer and hope it goes away
B.Delete the red and blue buttons from the game
C.Check only the code for the blue button, since that's the last action
D.Carefully repeat the exact sequence of actions and use 'say' blocks to check variables at each step
Challenging
A sprite's position is controlled by a 'forever' loop that smoothly moves it. You also have a 'When space key pressed' event to make it jump to a new location. When you press space, the sprite jumps but is immediately pulled back by the 'forever' loop. How can you fix this?
A.Make the 'forever' loop run faster
B.Remove the 'forever' loop completely
C.Use a variable (e.g., 'is_jumping') to tell the 'forever' loop to temporarily stop moving the sprite
D.Press the space key harder
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