Scratch

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Scratch  is a free visual programming language. Scratch is used by students, scholars, teachers, and parents to easily create animations, games, etc. and provide a stepping stone to the more advanced world of computer programming. It can also be used for a range of educational and entertainment constructionist purposes from math and science projects, including simulations and visualizations of experiments, recording lectures with animated presentations, to social sciences animated stories, and interactive art and music. Viewing the existing projects available on the Scratch website, or modifying and testing any modification without saving it requires no online registration.

Scratch allows users to use event-driven programming with multiple active objects called sprites. Sprites can be drawn, as vector or bitmap graphics, from scratch in a simple editor that is part of Scratch, or can be imported from external sources, including webcams.

As of 2013, Scratch 2 is available online and as an application for Windows, OS X, and Linux (Adobe Air Required). The source code of Scratch 1.x is released under GPLv2 license and Scratch Source Code License.

Origin of name
“Scratching” in the language of computer science means to reuse code that can be beneficial and effectively used for other purposes and easily combined, shared and adapted to new scenarios, which is a key feature in Scratch – “remix”, in which users can download and build up on public projects uploaded and developed by other users. It also gives credit to the participant who built on the original work and to the participant who created the original program. The name was derived from turntablism's technique of scratching (i.e., mixing sounds), relating the ease of mixing sounds to the ease of mixing projects made with Scratch. This research advanced understanding of the effective and innovative design of new technologies to enhance learning in after-school centers and other informal-education settings, and broadened opportunities for youth from under-represented groups who became designers and inventors with new technologies. Scratch was iteratively developed based on ongoing interaction with youth and staff at Computer Clubhouses. The use of Scratch at Computer Clubhouses served as a model for other after-school centers demonstrating how informal-learning settings can support the development of technological fluency, enabling young people to design and program projects that are meaningful to themselves and their communities.

The MIT Media Lab's Lifelong Kindergarten group, led by Mitchel Resnick, and its Montreal-based consulting company Playful Invention Company, co-funded by the latter with Brian Silverman and Paula Bonta, together developed the first desktop-only version of Scratch in 2003. Its purpose was to aid young people, mainly for ages 8 and up, to learn programming.



Scratch 2 was released in May 2013. With its introduction, custom blocks can be defined within projects.

In 2015, the Scratch homepage was updated with a new theme. As of January 17, 2016, only the homepage had been updated with this new theme and the rest of the site continued to use the old theme.

Educational use
Scratch was made popular in the UK through Code Clubs. These use Scratch as the introductory language because of its relative ease to make interesting programs and because skills learnt through Scratch can be applied to other basic programming languages like Python and Java.

Scratch is not exclusively for creating programs, since it provides a lot of visuals, programmers can create animated stories such as “The Pizza Dude”, “Haiku”, or “Gemclan”. For older students, they can use Photo Journalism that teaches the basic background of journalism. Students that want to specialize in math can use Lemonade Stand, “Dino Odd and Even”, “Data Workshop”, or “Ellipserator” that mainly focuses on geometry. Scratch flexibility allows teachers to create conceptual and visual lessons and science lab assignments, as Scratch is a useful tool to create animations that help visualize difficult concepts such as plant cell mitosis, water cycle, Galileo Thermometer and Hooke’s Law Experiment. Within the social sciences, instructors can create quizzes, games and tutorials that stimulate the mind and interact with the student. Using Scratch allows young people to understand the logic of programming and how to creatively build and collaborate. Scratch lets students create "meaningful personal as well as educational projects" which allows students a "practical tool" to express themselves after learning to use the language.

Harvard University lecturer Dr. David J. Malan prefers using Scratch over commonly used introductory programming languages, such as Java or C, in his introductory computer science course. However, there is a limited benefit in a college level education. Malan switches his course’s language to C after the first week.

User interface


From left to right, in the upper left area of the screen there is a stage area, featuring the results (i.e., animations, turtle graphics, etc., everything either in small or normal size, full-screen also available) and all sprites thumbnails listed in the bottom area. The stage uses x and y coordinates, with 0,0 being the stage center.

There are many ways to create personal sprites and backgrounds. First, users can draw their own sprite manually with "Paint Editor" provided by Scratch. Second, users can choose a Sprite from the Scratch library that contains default sprite, user’s past creations, a picture using a camera, or clip art.

With a sprite selected in the bottom-left area of the screen, blocks of commands can be applied to it by dragging them from the Blocks Palette onto the right area of the screen, containing all the scripts associated with the selected sprite. Under the Scripts tab, all available blocks are listed and categorized as the Motion, Looks, Sound, Pen, Data, Events, Control, Sensing, Operators, and More blocks as shown in the table below. Each can also be individually tested under different conditions and parameters via double-click.

Besides the Script tab, there are two additional tabs, the Costumes tab and the Sounds tab. An expandable bar at the right is Help area.

Next to the Scripts tab, there is the Costumes tab, where user can change the look of the sprite in order to create various effects, including animation. And the last tab is the Sounds tab, where users insert sounds and music to a sprite.

In comparison to the previous versions of Scratch, the areas have been rearranged in version 2.0, as previously the blocks palette was in the left area, the selected sprite area and scripts area associated with a selected sprite were in the middle of the screen, and the stage area with sprites thumbnails listed below it were in the right area of the screen.

Community of users


Scratch is used in many different settings: schools, museums, libraries, community centers, and homes. Its users are mostly kids aged 9–16. Scratch is also used in some introductory computer science classes (including Harvard's introductory computer class).

There is an annual "Scratch Day" declared in May each year. Community members are encourage to host an event on or around this day, large or small, that celebrates Scratch. These events are held worldwide, and a listing can be found on the Scratch Day website.

Via localization files downloaded with Scratch its interface language can be changed to a language of choice since Scratch is used in different parts of the world.

The Johns Hopkins University Center for Talented Youth offers an online course on Scratch programming for students in grade 6 and up through the CTYOnline program.

Empirical studies were made of various features—those that interfered with intuitive learning were discarded, while those that encouraged beginners and made it easy for them to explore and learn were kept. Some of the results are surprising, making Scratch quite different from other teaching languages (such as BASIC, Logo, or Alice).

Online community
The Scratch online community's slogan "Imagine, Program, Share" indicates that sharing and the social aspects of creativity are important parts of the philosophy behind Scratch. A few influential members of the Scratch online community made great personal strides in innovative methods with scratch programming.

Scratch projects are not seen as "black boxes", but as objects for remixing to make new projects. Projects can be uploaded directly from the development environment to the Scratch website and any member of the community can download their full source code to study or to remix into new projects. Members can also create project studios, comment, tag, favorite and "love" others' projects, follow another member to see their projects and activity, and share ideas. Projects range from games to animations to practical tools. Chat rooms are not allowed. All projects on the website are shared under a Creative Commons attribution and share-alike license and can be played in a web browser (using the Flash Player, which is unavailable for iOS devices).

The website receives over 125 million page views per month and as of April 10, 2016 it had 11,207,52 registered members (however, only 200,000 users created a project within the last month), and over 14,000,000 projects and growing rapidly.

The website frequently establishes "Scratch Design Studio" challenges to encourage creation and sharing by providing users with a basic design concept. There are custom home pages for Mexico and Israel that display local content in some sections of the home page. Scratch has participated in Hour of Code several times. There are also local independent Scratch websites in countries such as Portugal and the United Arab Emirates. In 2008, the Scratch online community platform (named "ScratchR") received an honorary mention in the Ars Electronica Prix. There is also an online community for educators, called ScratchEd. Scratch is also a fun literary structure, with online roleplays, in many different genres.

Features and derivatives
The current version of Scratch does not treat procedures as first class structures and has limited file I/O options with Scratch 2.0 Extension Protocol; an experimental extension feature that allows interaction between Scratch 2.0 and other programs. The Extension protocol allows interfacing with hardware boards such as Lego Mindstorms or Arduino. In addition Scratch 2 only supports one-dimensional arrays, known as "lists". Floating point scalars and strings are supported as of version 1.4, but with limited string manipulation ability. There is a strong contrast between the powerful multimedia functions and multi-threaded programming style and the rather limited scope of the Scratch programming language. On May 6, 2013, Scratch closed for 3 days to update to Scratch 2.0. The update changed the look of the site and included an online project editor. A new beta version of the Scratch 2 Offline Editor is currently available. This version replaces the old Scratch 2.0.

A number of Scratch derivatives called Scratch Modifications have been created using the source code of Scratch version 1.4. These programs are a variant of Scratch that normally include a few extra blocks or changes to the GUI.

In July 2014, a program called ScratchJr was released for iPad. Although it was heavily inspired by Scratch and co-led by Mitch Resnik, the original creator of Scratch, it is nonetheless a complete rewrite designed for younger children.

Some of them additionally introduce shifts in underlying approach to computing, such as the language Snap!, featuring first class procedures (their mathematical foundations are called also lambda calculus), first class lists (including lists of lists), and first class truly object oriented sprites with prototyping inheritance, and nestable sprites, which are not part of Scratch. Snap! (its previous version was called BYOB) was developed by Jens Mönig with documentation provided by Brian Harvey  from University of California, Berkeley and has been used to teach "The Beauty and Joy of Computing" introductory course in CS for non-CS-major students.

The source-code of Scratch and its derivatives are based on Squeak, which is based on Smalltalk-80. Version 2 of Scratch is implemented in ActionScript, with an experimental JavaScript-based interpreter being developed in parallel.

Catrobat is a visual programming language for smartphones and tablets inspired by Scratch. Pocket Code is an app with which you can create, download and upload programs created in Catrobat. Catrobat and Pocket Code are released under open source licenses.