Page 4: Making Your Own Block

Unit 1, Lab 2, Page 4

On this page, you will create a newgossip response block to make the program feel more like a conversation.
gossip2 reporting 'Guess what. Gabrielle helped Señora'

  1. If it isn’t open already, open your U1L2-Gossip project.

  2. Create the gossip response block:

Making a New Block

    image of 'Make a block' dialog box with 10 palette menus (Motion, Looks, Pen, Sound, Lists, Control, Sensing, Operation, Variables, Other) labeled 'Choose a color (a palette)'; a text box labeled 'Type a title for your block.'; three block shape options (puzzle-shaped/'Command', oval/'Reporter', and hexagonal/'Predicate') labeled 'Select a shape.'; two radio boxes (for all sprites, which is checked, and for this sprite only, which is not checked) with no label; and two buttons ('OK' and 'Cancel') labeled 'Click OK.'

  1. Create a new block by either clicking make a block button near the end of the palette, clicking the + sign in the top right corner of the palette (shown below), or right-clicking (or control-clicking on a Mac) in an empty spot in the scripting area and choosing “make a block…” (shown below).
    plus sign atop palette make a block option
  2. Choose the color, in this case red for Lists.
  3. Type the title for your block: gossip response.
  4. Select the shape and click OK. For this block, choose the oval reporter shape because you want it to report a value (the chosen response) to another block.

Because you chose the reporter shape, the block editor opens with a report block already attached to the hat block. Whatever input you give to report will become the value reported by your new block.

Coding the Block’s Script

  1. Drag in the blocks you need. For your new block, use the list block and item(1) of (). Use the value reported by list as an input to item.
  2. Snap the blocks together. The code’s structure will be just like the code inside who, does what, and who 2.

  3. Fill all the inputs.

    • For this project, click the down-arrow in item to change “1” to “random”.
    • Then fill list with phrases like “Guess what,” “I heard,” or “Who cares!”
  4. Click OK when you’re satisfied.

: Procedures, Reporters, and Commands

A procedure is a named sequence of instructions that may take inputs and may report a value. Some languages call procedures methods or functions. Here are two types of procedures you have seen in Snap!:

  • Reporters have an oval shape. They report a value.
    pick random () to () list () () + ()

  • Commands have a jigsaw puzzle shape. They tell the computer to do something without reporting a value.
    broadcast () point in direction () say ()

  • The procedure PROCEDURE double (x) { RETURN (2 * x) } would be written as

    PROCEDURE double(x)
  {
  RETURN(2 * x)
  }

    or PROCEDURE double(x) { RETURN(2 * x) }.

  • Many languages (and the AP CS Principles Exam) use return instead of report as the name of the command to give a value back at the end of a function call.

  • The exam uses “value of a procedure” to mean the value the procedure returns when called. For example, “the value of double(5)” means 10.

Debugging

  1. Test your custom gossip response block by clicking it several times. It should behave like the who, does what, and who 2 blocks. Debug any problems before moving on.

Review how to edit a block in Unit 1 Lab 2 Page 2: Customizing and Debugging, if needed.

  1. Use your new block: Edit gossip 2, and insert gossip response in place of the text “Oh, but….”
    gossip 2 { report (join (gossip response) ( ) (who 2) ( ) (does what) ( ) (who) ) }

Why do I see plus signs around gossip 2 in Snap! but they’re not in this picture?

Normally, when you are using the Block Editor, you see plus signs because you have to click on them to add inputs to your blocks. But to show you the finished code here, it looks cleaner without the plus signs.

  1. Test and debug gossip 2 also.

  2. Then test the whole program by clicking script D several times, and fix any bugs. Save your work