Conditionals & Boolean Statements

Understanding Conditionals

In programming, a conditional is a statement that allows your code to make decisions. It's like asking a question and then doing something based on the answer. In Scratch, we use conditionals to make our sprites react to different situations.

How Conditionals Work

A conditional typically follows this pattern:

• If (some condition is true)
• Then (do this)
• Otherwise (do something else)

In the demo above, we're using a conditional to check if the light is on or off. Based on this condition, we either show a bright or dark room. This is a simple example of how conditionals can change the behavior of our program.

If Statements

An "If" statement is the most basic type of conditional. It allows you to execute a block of code only if a certain condition is true.

The "If" Block in Scratch

In Scratch, the "If" block looks like this:

Example: Moving a Sprite with Arrow Keys

Let's create a simple script that moves a sprite when an arrow key is pressed:

1. Drag an "If" block into your script area.

2. From the "Sensing" category, drag a "Key [space] pressed?" block into the condition of the "If" block.

3. Change "space" to "right arrow" in the dropdown menu.

4. Inside the "If" block, add a "Move 10 steps" block from the "Motion" category.

In this example, we've used "If" statements to check which arrow key is pressed and move the sprite accordingly. Try pressing the different arrow buttons to see how the sprite moves!

If-Else Statements

An "If-Else" statement allows you to execute one block of code if a condition is true, and a different block of code if the condition is false.

The "If-Else" Block in Scratch

In Scratch, the "If-Else" block looks like this:

Example: Changing Sprite Color Based on Position

Let's create a script that changes a sprite's color based on its position:

1. Drag an "If-Else" block into your script area.

2. From the "Operators" category, drag a "[ ] > [ ]" block into the condition of the "If-Else" block.

3. From the "Motion" category, drag an "x position" block into the first space of the ">" block.

4. Type "0" into the second space of the ">" block.

5. Inside the "If" part, add a "Set color effect to 0" block from the "Looks" category.

6. Inside the "Else" part, add another "Set color effect to 50" block.

In this example, we've used an "If-Else" statement to change the sprite's color based on its x-position. If the sprite is on the right side of the stage (x > 0), it turns one color. Otherwise, it turns a different color. Try moving the sprite left and right to see the color change!

Guided Tutorial: Creating a Simple Game with Conditionals

In this tutorial, we'll create a simple game where a sprite tries to catch falling objects. We'll use conditionals to control the sprite's movement and detect collisions.

Step 1: Setting Up the Stage

1. Create a new Scratch project.

2. Choose a backdrop for your game. You can use the default backdrop or choose a new one from the library.

Step 2: Creating the Player Sprite

1. Choose a sprite for the player. This will be the character that moves to catch falling objects.

2. Add the following script to control the player's movement:

when green flag clicked
forever
    if <key [left arrow] pressed?> then
        change x by -10
    end
    if <key [right arrow] pressed?> then
        change x by 10
    end
    if <touching [edge v]?> then
        if <(x position) > (0)> then
            set x to (240)
        else
            set x to (-240)
        end
    end
end

Step 3: Creating the Falling Object

1. Add a new sprite that will be the falling object. You can use any sprite you like.

2. Add the following script to control the falling object:

when green flag clicked
forever
    go to x: (pick random (-240) to (240)) y: (180)
    repeat until <touching [edge v]?>
        change y by -5
        if <touching [Player v]?> then
            change [score v] by (1)
            play sound (pop)
            wait (0.1) seconds
        end
    end
end

Step 4: Adding a Score

1. Create a variable called "score" for all sprites.

2. Add the following script to initialize the score:

when green flag clicked
set [score v] to (0)

Congratulations! You've created a simple game using conditionals. The player sprite moves left and right based on key presses, and the falling object resets its position when it touches the edge or the player. The score increases each time the player catches the falling object.

Try playing the demo above to see how the game works. You can move the player left and right using the buttons, and try to catch the falling object to increase your score!

Mini-Project: Create a Maze Game with Conditionals

Now it's your turn to create a project using what you've learned about conditionals. You'll be creating a simple maze game where a sprite navigates through a maze using arrow keys.

Project Description

Create a Scratch project where a sprite navigates through a maze. The sprite should move with arrow keys and stop when it hits a wall. When the sprite reaches the end of the maze, it should display a "You Win!" message.

Step-by-Step Guide

1. Create a new Scratch project and design a simple maze as the backdrop.

2. Add a sprite that will navigate through the maze.

3. Use "If" statements to move the sprite when arrow keys are pressed.

4. Use an "If-Else" statement to check if the sprite is touching a wall. If it is, move it back slightly.

5. Add another conditional to check if the sprite has reached the end of the maze.

6. Display a "You Win!" message when the sprite reaches the end.

Example Code Structure

when green flag clicked
forever
    if <key [right arrow] pressed?> then
        point in direction (90)
        move (5) steps
    end
    if <key [left arrow] pressed?> then
        point in direction (-90)
        move (5) steps
    end
    if <key [up arrow] pressed?> then
        point in direction (0)
        move (5) steps
    end
    if <key [down arrow] pressed?> then
        point in direction (180)
        move (5) steps
    end
    if <touching color [#000000]?> then
        move (-5) steps
    end
    if <touching color [#00FF00]?> then
        say [You Win!] for (2) seconds
        stop [all v]
    end
end

Challenge

Can you add a timer to your maze game? Use a variable to keep track of time, and display how long it took the player to complete the maze. You might need to use some additional conditionals to start and stop the timer at the right moments!

Remember, creativity is key! Feel free to add your own twists to the maze game. Maybe add collectibles, multiple levels, or even enemies to avoid. Don't forget to share your project with your classmates when you're done!