Variable

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This article is about Scratch variables in general. For other uses, see Variable (disambiguation).

(variable::variables)

The variable reporter
block in Scratch 3.0.

The "Make a Variable" button

A variable is a changeable value recorded in Scratch's memory. Variables can only hold one value at a time, unlike lists. These values can be either numbers or strings — any text. Clicking on an isolated variable in the scripts area displays a small bubble reporting the value of the variable. Unlike many other programming languages, Scratch does not allow variables to be created by a script as it runs. Instead, variables are created with the "Make a Variable" button in the Block Palette. Lists allow multiple values to be stored, acting like a group of variables.

Variables Blocks

There are five different blocks relating to variables:

Note:

Click on a block to find out more.

• (variable) // This is the block that reports the value of a variable
• set [variable v] to (0) // This sets a chosen variable to a specified value
• change [variable v] by (1) // This changes the value of a chosen variable by a specified amount
• show variable [variable v] // This shows the specified variable in the project player
• hide variable [variable v] // This reverses the 'show variable' block

Types

There are three types of variables. All variables are stored in RAM, and default to the values in the file the project originates from (project.json). Variable changes are saved with the project and do not reset on green flag.

Global Variables

By default, when a variable is created, it is a global variable. Global variables can be read and changed by any sprite, including the Stage. Opening the project.json file in the SB3 shows that global variables are stored by the stage.

Local Variables

Local, (or private/personal) variables are created the same way as global, but another option is selected in the variable creation dialog, "For this sprite only". Local variables are stored independently by each sprite or clone can only be changed by their owner, but can be read by other sprites using the () of () block. The Stage cannot have local variables.

Local variables are extremely useful when a template sprite that needs to be duplicated and edited is wanted. For example, in a game where one must pop bubbles, a "bubble" sprite should be made which has personal variables like "speed" and should be programmed independently. Then it should be duplicated until there are enough bubbles. Since each bubble has an individual "speed" variable, they will not interfere with each other unlike if "speed" was a global variable.

Note:

Clones inherit local variables into their properties, meaning that each clone has a separate number for the local variable. The clone will still keep the value of the variable, but it can change it. This is also useful in the same way.

Cloud Variables

Main article: Cloud Data

Cloud variables are variables that are stored on Scratch's server. When a cloud variable updates, it does so across all instances of the project open, and it also gets saved for the next time the project is opened. Cloud variables have a small cloud icon next to their names. In Scratch 3.0, cloud variables only support numerical data and all are limited to 256 digits, one project can only hold maximum of 10 cloud variables, after that the cloud variable checkbox is greyed out. While it is possible to make chat rooms with cloud variables, it isn't allowed because it would be too hard to moderate.^{[citation needed]}

Note:

If a cloud variable has been changed, the user must wait 0.1 seconds before it can be changed again.

Uses

Main article: What can I use variables for?

Setting the slider min and max.

The checkbox to show/hide a variable in 3.0.

Variables are used whenever a value must be stored — e.g., if a project required the user to input a name and then remember that name, the name would be stored in a variable. With this, the name can be retrieved at any time; all the project has to do is check the value (which is the name).

The look of the variable monitor can be changed into three forms: The normal readout, the large readout, and the slider. The form of the variable can be changed by double-clicking or right-clicking it and selecting the option that is wanted.

The normal readout contains the title and the value, the large readout only contains a value, and the slider is similar to the normal readout, but has a slider on it. If the slider is chosen, there will be another option once right-clicked called "Change slider range." Choosing it will allow the user to set the range of the slider.

It can be chosen whether to hide or show a variable on the stage by clicking the tick box in the variable panel.

Length Limit

In Scratch 2.0, there was a character limit of 10240. This limit was removed in Scratch 3.0.

Glitch Variables

This article or section documents something not included in the current version of Scratch (3.0). It is only useful from a historical perspective.

Some examples of the glitch variables

Green flag/stop sign glitch variables

Glitch variables could be made by naming them with names including %d (direction drop down/number insert), %s (text input), %m (variable drop down), %b (boolean), %n (number input), or %c (color input), which will look like those at the left. This is because Scratch reads the percent sign followed by certain letters as an argument. By naming a variable @greenFlag or @stop it will display a green flag or a stop sign, respectively, as seen at the right. Also, the codes @turnRight and @turnLeft create a rotate sign, right or left.

This bug was patched in v423 of Scratch 2.0 and no longer works.

Lists

Main article: List

A list is made of items — each item like a variable. Lists can be useful when many variables are needed or when the amount of memory that needs to be stored can not be determined by the programmer before the project is run. However, lists can only store 200,000 items and not more.

Cloud Lists

Cloud lists do not exist in Scratch 3.0. It has been suggested many times and is rejected by the Scratch Team. Cloud lists, if they existed, would be accessible by all Scratchers via the cloud server.

Some Scratch Modifications contain cloud lists. Some projects also contain cloud lists, although they are very hard to make and most of them usually break in new versions of Scratch. The only way to make one is to encode and decode lists into and from cloud variables, but this is very limited because variables are restricted to 256 digits.

Types of Readouts

Main article: Variable Monitor

The three different variable displays in Scratch 3.0.

If a variable stage monitor is right-clicked, a menu shows up with three options: normal readout, large readout, and slider. There is also a show/hide option. In Scratch 1.4, the selected option had two asterisks (*) around it.

Examples

Variables are used in numerous projects to keep score, show health, connect with players, or list some friends. Here are some projects that use variables:

• griffpatch's "massive multiplayer platformer" game uses cloud data to connect players.
• LBMCompany's virtual telescope project uses variables to tell how many stars there are on the screen.
• MooShoeGaming's "The Front" project used variables as "True or False" statements to tell if the player is still alive.
• djpro's guide to making platformer games has to have variables for the ball to move and jump as if gravity was affecting it.

Those were only a few examples of variables used in programs; variables are used widely in different projects around Scratch, and most more advanced projects use them.

See Also

• Variables Blocks
• Lists
• Stage Monitor
• Cloud Data

External Links

• Variable on Wikipedia
• Input Type Specifiers