Conditionals & Boolean Statements

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.

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:

The "If" block in Scratch

Example: Moving a Sprite with Arrow Keys

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

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!

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:

The "If-Else" block in Scratch

Example: Changing Sprite Color Based on Position

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

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!

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

Step 2: Creating the Player Sprite

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

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

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!

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

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!