Control Programming : Turtles

A turtle is a small robot that can move around the floor. The turtle can move forwards and backwards and rotate left and right. Attached to the turtle is a pen. If the pen is lowered then the turtle will draw on a piece of paper placed underneath it as it moves. If the pen is raised then the turtle will not draw as it moves.

To carry out a task the turtle must be given a sequence of instructions to follow. The sequence of instructions is known as a program. A special programming language is used to give these instructions. Each individual instruction is called a command . Most turtles can be programmed using a language called Logo. The most basic turtle control language will support these six commands :

Logo Control Commands
Command Purpose
PENDOWNLower the turtle's pen to start drawing.
PENUPRaise the turtle's pen to stop drawing.
FORWARD 50Go forward 50 steps.
BACK 100Go back 100 steps.
LEFT 90Turn left 90 degrees.
RIGHT 45Turn right 45 degrees.

The number after a forward or backward command is how many steps the turtle should move. The number after a left or right command tells the turtle how many degrees to turn through.

If a robot turtle is not available then the operation of the robot can be simulated by using a picture of a turtle on the screen.

Here are some example programs which use the turtle to draw shapes.

GCSE ICT Companion 04 - (C) P Meakin 2004