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In what order does Scratch execute commands

Contributed by Dimitris Nikolos, April 10, 2010
In what order does Scratch execute the commands when they are placed in threads???
  • Original Author: Nikolos Dimitris
  • Education Level: Preschool and Kindergarten, Elementary School, Middle School, High School, College and University, Professional Development, Other
  • Content Types: Activity, Assessment, Handout, Sample Scratch Project
  • Curricular Areas: Computer Science, Engineering, Language Arts, Mathematics, Music, Science, Social Studies, Teacher Education, Technology, Visual Arts, Other
  • Keywords: parallelism, sequence, concurrent programming

Students are exposed to the following Scratch project.

 

They are asked to execute every thread using double click. The result is that all the commands are executed sequentially and canonical polygons are drawn.

Canonical polygons

 

Then they are asked to use the green flag to run the program. The following shape is drawn.

 

A not canonical shape

Students are asked why this is the case.

In order to find out what "went wrong" they are shown the single stepping setting.

 

After that they should be able to recognize that "parallel" threads are executed in an arbitrary manner, and they may be able to correct the program in order to draw the canonical polygons.

 

This activity is summarized in this project (project made in greek).

 

 

 

Resource Files
application/octet-stream iconThe first project
Links: 
A project that summarizes the activity