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Lesson 3: Using [If then] blocks

In the Disk Maze Challenge, the VR Robot is checking the condition of the Front Eye Sensor to see what color is being reported. Each of the colors matches to a different behavior the VR Robot should perform.

block with object color
  • Start a new project and name it Unit7Lesson3.
    Unit7Lesson3 Named
  • Drag an [If then] block into the workspace and attach it to the [When started] block.
    when started

    For Your Information

    The [If then] block is a C block that accepts Boolean reporter blocks as input. Using the patterns observed while solving the Disk Maze in Lesson 2, a project can be created where the VR Robot makes a decision if the condition reports as TRUE or FALSE.

    boolean values

    The [If then] block will run one time in a project. In this example, the Front Eye Sensor will report TRUE if a green object is detected, and execute the command inside the C block - turn right for 90 degrees. If a green object is not detected, the project will move to the next command in the stack.

    if then example
  • Drag a <Color sensing> block into the workspace into the hexagonal input of the [If then] block.
    add if then
  • Change the parameter of the <Color sensing> block to ‘green.’
    change to green
  • When the Front Eye Sensor detects a green disk, the VR Robot will need to turn right 90 degrees to begin solving the Disk Maze. Drag a [Turn for] block into the [If then] block.
    turn right green
  • Follow these same steps to add another [If then] block for all three colors in the Disk Maze (green, blue, and red). Each color is associated with a different behavior. The blocks inside the [If then] block will need to match that intended behavior. Add the following blocks to the project. When the VR Robot detects the color ‘blue,’ the VR Robot will turn left 90 degrees.
    detects blue
  • When the VR Robot reaches the end of the maze, the VR Robot will detect the color ‘red.’
    detects red
  • To stop the VR Robot, another [If then] block needs to be added with instructions for what to do when the VR Robot detects ‘red.’ Add the following blocks to the project.
    add detects red
  • The VR Robot can also make a decision if it does not see a color by using the ‘none’ value. At the starting point of the Disk Maze, the VR Robot does not detect any colors.
    Front Eye Detection
  • Because the Front Eye Sensor does not detect a color at the beginning of the Disk Maze, the VR Robot will need to drive forward until it detects the green disk. Another [If then] block can be added to instruct the VR Robot for what to do when no color is detected.
    detects none
  • Add the following blocks to the project. When the VR Robot does not detect any color, the VR Robot will drive forward.
    add detects none
  • The VR Robot now has instructions for each color detected by the Eye Sensor.
    • Front Eye Sensor detects ‘green?’
      • Turn right 90 degrees
    • Front Eye Sensor detects ‘blue?’
      • Turn left 90 degrees
    • Front Eye Sensor detects ‘red?’
      • Stop driving
    • Front Eye Sensor detects ‘none?’

      • Drive forward
  • Open the Disk Maze Playground and run the project.

Select the Next button to continue with the rest of this Lesson.