Summer Computing Workshop

Session 2

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)

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 isn’t already written, click in the small text field within the block and type the question “What’s your name”.

Now drag a block and join it to the bottom of the block

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 let’s construct the example. (see example 2.1 on the Constructed Examples page at the end of this section)

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 doesn’t 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 doesn’t perform the action if the type is incompatible. It is difficult for the sprite to move “word” steps.

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

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)

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)

Constructed ExamplesExample 2.1

Example 2.2

Example 2.3

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.

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?