The Scratch programming environment
An algorithm is a clear sequence of commands for an executor to carry out. The executor can be a person, robot, machine or computer. An algorithm can be written as text, a formula, a flowchart or a program. A program is a sequence of commands written in a language the computer understands, and programming languages are the special languages programs are written in. Scratch is a free visual programming environment for children and beginners (created by a team at MIT): you do not type code, you snap coloured blocks together like puzzle pieces. The Scratch window has a blocks palette (categories by colour: Motion, Looks, Sound, Events, Control, Sensing, Operators, Variables), a script area, the stage and the sprites pane. There are tabs: Code, Costumes and Sounds. The stage is 480 wide and 360 high: the x axis runs from –240 to 240, the y axis from –180 to 180, and the centre is (0, 0). A program starts with the green flag and stops with the red stop button. When joining the online Scratch community, sign up with the help of a teacher or an adult and do not use your real name or personal details.
“Robot pupil”: one pupil is the executor (robot); the class gives step-by-step orders (“3 steps forward”, “turn right”) to guide them past obstacles. If an order is unclear, the robot says “I don’t understand”.