14.2. Using Decisions with Turtles

Here’s an example of conditional execution (using an if statement) with a turtle. We can make the turtle do some action when a condition is true. In this example if the turtle gets to right side of the space (drawing area), pick it up and move it back to the left side of the space further down so that it can draw more.

This code calculates maxX as half the width since the drawing area uses the cartesian coordinate system with (0,0) as the center. Since the width is 400 the maxX is 200. We move the turtle to -1 * maxX which is -200. When the turtle’s x coordinate is greater than or equal to the maxX, which means it is at the right edge, then we move the turtle back to the left edge and down 100.

For more information on what this code does listen to the audio tour.

Modify the code above to draw a different pattern. Try turning changing the direction of every turn, what does that do?


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