ITEC 109 2014spring ibarland

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lab-turtles-cont
Turtles
functions calling functions

We will continue our work with turtles from last time. Review / Re-explore the menu JES > Turtles: What function creates the world? WHat function creates a Turtle? What info do you need to pass in to each function?

• Let's draw a triangle together, in class (just calling functions via the interactions pane), arranging to leave the turtle pointing in its original direction.

  bonus thought: How many degrees did we end up turning, altogether? 360° -- the turtle rotated exactly once while drawing the figure! If you wanted to make a pentagram or a 19-sided figure instead, can you guess how much each of the individual (5 or 19) turns should be?

• Like we did for square last time, turn these statements into a function which takes a turtle and a size, and draws a triangle of the indicated size.

  Note:After calling your function, leave the turtle facing the same direction as it started.

• Write a new function which has the turtle draw a (crude) radiation-warning symbol. Hint: This is an example of having your function call other functions you've previously written!
  
• Optional: Make a function which (given a turtle-object) makes several triangles of different sizes right on top of each other.
• Write a series of statements (in the top window) to have a turtle draw the following 'zag' shape, where the distance from the start to the finish is 90. (How big is the gap, if the zaggy part outlines an equilateral triangle?)
  
• Now, upgrade your zag function so that it takes in a Trtl and a distance, and has the Trtl draw that zag shape, where the total distance covered from the start to the finish is the provided distance.

 

 

• Here's a bigger task: Make a function smiley that takes in Trtl and a size, and makes a smiley face like: (Note that the smile doesn't have to exactly line up with the eyes; it can be a bit off, to add to the creepy factor.)

  How, exactly, will you draw the bowtie-ish thing, using two triangles? You must obey the first law of programming: No Repeated Code. If you want to (say) draw some triangles, just call the function you already wrote previously -- Easy!

  hint:Have the turtle start in the middle of the bowtie-thing.

  Note: your next problem is easier, if you decide that smiley leaves the turtle facing the same direction it started.

  How do you have one turtle draw two things which aren't next to each other? We need to move the turtle without drawing. Remember, the turtles have a pen tied to their tail; explore the menu JES > Turtles for functions which can lift/lower the pen.

• Finally: Use your previous function to make a function threeSmileys which draws something like:

to teacher:

Common bug: Sometimes in threeSmileys, just one of them is mysteriously missing its eyes!?! This is because penUp and penDown have been called from several different functions and not restored.

(It's a casualty of using void methods and side-effects: our turtle has state that we're not specifying; perhaps every method should return a Trtl structure, and unit-tests could test that all fields of the returned Trtl were the expected result.)

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©2014, Ian Barland, Radford University Last modified 2014.Feb.24 (Mon)

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