1.2 Scr0320: memory, variables, and literals in scratch 2.0  (Page 6/11)

No sprites

There are a few things that we can conclude by viewing Image 1 . First, there are no sprites in this program. The program consists solely of

• The Stage, shown in white in the upper left,
• A small program consisting of three scripts shown in the rightmost panel,
• Two variables shown in orange near the middle of the center panel and also shown in gray/orange in the upper-left corner of the Stage.

The toolbox buttons

If you have worked through some Scratch v2.0 examples, you will recognize that the material in the lower-center panel is always associated with one of the followingten toolbox buttons in the upper-center panel:

• Motion
• Looks
• Sounds
• Pen
• Data
• Events
• Control
• Sensing
• Operators
• More Blocks

In other words, when you click on one of the ten buttons in the upper-center panel, it exposes a set of tools that you can use to write your program. Those toolsappear in the lower-center panel.

When one of those ten buttons is clicked, it becomes completely colored and the tools associated with that button are displayed below it. The orangebutton labeled Data has been selected in Image 1 .

The Data toolbox

The lower-center panel of Image 1 presents the Data toolbox showingthe tools that are exposed by the Databutton.

Tools in the Data toolbox: When you first click the Data button, only two gray buttons are exposed in the toolbox. One gray button is labeled Make a variable and the other gray button is labeled Make a list . The two orange variables and the orange tools shown in the Data toolbox of Image 1 were produced by clicking twice on the button labeled Make a variable and entering a name for each variable.

Create two variables

Click here for detailed instructions on creating variables.

Image 1 shows that this Scratch program contains two variables with the following names:

• Counter
• counter

I purposely spelled the names of the two variables the same and made them differ only by the case of the first letter to illustrate that Scratch is casesensitive insofar as the names of the variables is concerned. Even though these two variable names contain the same letters, they are two different variablesbecause one name begins with an upper case "C" and the other name begins with a lower-case "c".

Allowable operations for variables

There are four programming blocks (in the Data toolbox of Image 1 ) associated with each variable. As you have probably learned from working through example programs, you can drag theseblocks into the programming area in the rightmost pane in Image 1 to actually write the program. Thus, there are four different operations that you can perform on a variable:

• You can set the value of the variable to a specified value.
• You can change the value of the variable by a specified value.
• You can show a variable on the stage.
• You can hide a variable.

(You can manually perform the last two operations by checking or clearing the checkboxes next to the variables but the bottom two tools allowyou to perform that operation as part of a running program.)

Specifying the values

After dragging a programming block from the Data toolbox into the programming area, you can: