Variables and Parameters

Variables in Scratch are like containers that can hold different types of information. They're useful for storing data that might change during your program's execution, such as a player's score or the number of lives remaining.

Creating a Variable

To create a variable in Scratch:

1. Click on the "Variables" category in the block palette
2. Click the "Make a Variable" button
3. Give your variable a name (e.g., "score")
4. Choose whether the variable is for all sprites or just for one sprite

Once you make a variable, Scratch adds an oval block with its name to the palette. This is the reporter block: it reports the value the variable is holding right now, and you can drop it into any other block that needs that value.

The reporter block for a variable

Using Variables

Once you've created a variable, you can use these blocks to work with it:

• Set [variable] to [value]: Sets the variable to a specific value
• Change [variable] by [value]: Increases or decreases the variable's value
• Show Variable: Displays the variable's value on the stage
• Hide Variable: Hides the variable from view on the stage

In this demo, we've created a simple score counter using a variable. Click the "Increase Score" button to add points, and "Reset Score" to start over. This demonstrates how variables can be used to keep track of changing values in your Scratch projects.

Parameters in Scratch are values that you can input into blocks to customize their behavior. They allow you to create more flexible and reusable code by changing the input without having to modify the entire block.

Common Parameter Blocks

• Pick Random [1] to [10]: Generates a random number between two values
• Ask [Question] and Wait: Prompts the user with a question and waits for input
• Say [Message] for [2] seconds: Displays a message for a specified duration
• Move [10] steps: Moves the sprite a specified number of steps

Blocks that take parameters, with each input slot labelled

Using Parameters

To use parameters effectively:

1. Identify blocks with input fields (usually rounded rectangles)
2. Click on the input field to change its value
3. You can enter numbers, text, or even use other blocks as inputs
4. Experiment with different values to see how they affect your project

In this demo, we're using parameters to control the random movement of a sprite. You can adjust the minimum and maximum number of steps the sprite can move. Click "Move Randomly" to see the sprite move a random number of steps within your specified range. This shows how parameters can make your projects more dynamic and interactive.

In this exercise, we'll create a simple quiz game that uses both variables and parameters. The game will ask the player questions, keep track of their score, and provide feedback.

Step 1: Setting Up the Variables

Step 2: Creating the Quiz Logic

Step 3: Adding Multiple Questions

Example Code Structure

when green flag clicked
set [Score v] to (0)
set [Question Number v] to (1)
repeat (3)
    if <(Question Number) = (1)> then
        ask [What is the capital of France?] and wait
        if <(answer) = [Paris]> then
            change [Score v] by (1)
            say [Correct!] for (2) seconds
        else
            say (join [Incorrect. The answer is ] [Paris]) for (2) seconds
        end
    end
    if <(Question Number) = (2)> then
        ask [How many continents are there?] and wait
        if <(answer) = [7]> then
            change [Score v] by (1)
            say [Correct!] for (2) seconds
        else
            say (join [Incorrect. The answer is ] [7]) for (2) seconds
        end
    end
    if <(Question Number) = (3)> then
        ask [What is the largest planet in our solar system?] and wait
        if <(answer) = [Jupiter]> then
            change [Score v] by (1)
            say [Correct!] for (2) seconds
        else
            say (join [Incorrect. The answer is ] [Jupiter]) for (2) seconds
        end
    end
    change [Question Number v] by (1)
end
say (join [Quiz complete! Your score: ] (Score)) for (5) seconds
                

This simple quiz game demonstrates how variables can be used to keep track of the score and question number, while parameters are used in the "Ask" blocks to pose different questions. Try playing the demo to see how it works!

Now it's your turn to create a project using what you've learned about variables and parameters. You'll be creating a customizable story generator that asks the user for inputs and then generates a short story based on those inputs.

Project Description

Create a Scratch project that asks the user for various inputs (like a character name, a place, an object, etc.) and then uses these inputs to generate a short story. Use variables to store the user's inputs and parameters to insert them into the story.

Step-by-Step Guide

Example Code Structure

when green flag clicked
ask [What is the main character's name?] and wait
set [character v] to (answer)
ask [Where does the story take place?] and wait
set [place v] to (answer)
ask [Name an object for the story.] and wait
set [object v] to (answer)
say (join [Once upon a time, ] (join (character) (join [ went to ] (join (place) (join [. There, they found a magical ] (join (object) [. The end.])))))) for (10) seconds
                

Challenge

Can you add more complexity to your story generator? Try adding conditional statements to create different story paths based on the user's inputs. For example, if the place is "forest", the story could involve encountering animals, while if it's "city", it could involve exploring tall buildings.

Remember, creativity is key! Feel free to expand on this basic structure to create more complex and interesting stories. You could add more variables, create longer stories, or even add illustrations that change based on the user's inputs. Don't forget to share your project with your classmates when you're done!