Programming with Scratch

1
Programming with Scratch

• Summer Computing Workshop

2
Session 2
3
Input in Scratch

• Multi-Character input - This is used when the
  user is prompted to enter a number or word.
• Problems with multi-character input - Possible
  problem with type differences
• Single-character input This is mainly used to
  key specific events (an example may be moving a
  sprite when an arrow key is pressed)

4
Asking Questions

• Now we will discuss how to ask the user for a
  word or number which can then be used in the
  script. We will do this by having the sprite ask
  the user his/her name and then replying using the
  name.
• Click sensing and drag an
  block to the center scripts menu. We
  want the program to start when the green flag is
  clicked so do what is necessary. If it isnt
  already written, click in the small text field
  within the block and type the question Whats
  your name.
• Now drag a block and
  join it to the bottom of the
  
  block

5
Asking Questions

• Since we want the sprite to answer with the name
  and a short sentence, we need the special block
  which is located in the
  operators section.
• The goal is to place something such as Great to
  meet you into the left text field. Drag the
  answer block (found in sensing) to the right text
  field. This joining is called concatenation.
• We want the join block inside of the say block so
  now lets construct the example. (see example 2.1
  on the Constructed Examples page at the end of
  this section)

6
Using number input

• Lets do a small project that uses a sprite to ask
  the user how many steps he/she wants the sprite
  to move (refer to example 2.1 if you need help)
• Now that we have a script that does this, what do
  you think will happen if we entered a word
  instead of a number? Try it and see if you were
  correct.
• The sprite doesnt move!! This brings up the
  topic of different data types. In Java, C, and
  other programming languages, the programmer must
  specify what type of data it is before the data
  can be used. In Scratch the two data types are
  words and numbers. Other programming languages
  may not properly run if data types are
  incompatible. Scratch runs the program but
  doesnt perform the action if the type is
  incompatible. It is difficult for the sprite to
  move word steps.

7
Movement blocks

• To enable the sprite to move by using single
  character input, we must first learn some of the
  most used motion blocks
• Drag a and a
  to the center section
• By using these blocks we can move the sprite any
  direction on the x and y axis.
• Change x moves the sprite along the x axis, a
  negative number left , a positive number moving
  it right
• Change y moves the sprite along the y axis, a
  negative number moving it down, a positive number
  moving it up

8
Single Character Input

• Now we have movement blocks on the screen, we
  only have two directions so we must duplicate
  both blocks so our sprite can move all four
  directions (up, down, left, right)
• After we have four blocks on the screen, change
  the number in one of the change x blocks to
  negative and the same for a change y block.
• Now drag a block
  to the center and duplicate it three times so we
  have a total of four
• Now we will construct the example (see example
  2.2 on the Constructed Examples page at the end
  of this section)

9
Single Character Input

• Now we will do an example using another simple
  new concept. The special block we will be using
  allows the user to change the direction the
  sprite is facing.
• First choose a sprite (preferably one that has a
  top down view)
• Drag four blocks to the center window
• Since we have 4 directions to move, we must have
  4 key pressed blocks and 4 move blocks
• All of these will work together to move the
  sprite and face the sprite in the direction the
  user entered
• Construct example (see example 2.3 on the
  Constructed Examples page at the end of this
  section)

10
Constructed Examples
Example 2.1
Example 2.2
Example 2.3
11
Session 2 Project

• Create a small animation using single and multi-
  character inputs. Use single-character input to
  key events or move a sprite about the screen.
  Use multi-character input to ask for a question
  , the Sprite must respond to the question using
  the answer to the question.

12
Session 2 Questions

1. What are two different types of input?
2. Scripts are made up of one or more _____?
3. Explain the flow of execution in a script/method.
4. For what might we use multi-character input?
5. For what might we use single-character input?