First, create a function called draw_square(side_length, angle). This function takes two integers as parameters: the length of a side of the square, and the angle that the turtle should start at when drawing the square. Recall that you can use the setHeading(angle) function of the turtles to automatically turn the turtle to a specified angle.

Once you the draw_square function written, try using this to draw two overlapping squares at the center of the turtle window. This is to just check and make sure that the draw_square function works.

Afterwards, create a function called draw_nautilus(num_squares, offset), which takes two integer parameters: the number of squares to draw in the sea-shell, and an offset. This offset can be used to both increase the side length of a square, and the heading of the turtle.

draw_nautilus should use a for loop to call draw_square several times. You should use the offset and loop variables in your computations for the parameters to the draw square function. This will assure that each loop iteration, your new squares would be drawn larger at increasing angles.

This activity is going to make extensive use of the moveTo function we discussed earlier. Make sure you fully understand how this function works before moving on.

The most important part of this activity is keeping track of where your turtle, and lines are in the coordinate system of the turtle world. Remember (0, 0) is the upper left hand corner of the turtle window.

Draw two lines perpendicular (at a 90° angle to one another) on the center of the screen. After drawing these lines, you should be able to define the points (x₁, y₁), (x₂, y₂) , and (x₃, y₃). Let (x₁, y₁) be the top most point, (x₂, y₂) be the point of intersection, and (x₃, y₃) be the point at the other end of the horizontal line.

Define a variable called number_of_lines, and store an integer which is the number of lines you want to draw in the curve. You can get how far from the end points (offset) you need to move for each line segment by dividing the length of the main lines by this variable.

Given this offset, you need to compute 4 new values: (x₄, y₄) and (x₅, y₅). (x₄, y₄) should be on your vertical line, so x₄ should be the x coordinate of the vertical line. The y coordinate should be the top most points's y value (y₁) plus the offset. (x₄, y₄) should be on the opposite (horizontal) line, so y₄ should be the y coordinate of that line. x₄ should be the corner x coordinate (x₂) plus the offset. You then just connect these points.

Using a loop, you can iterate how many offsets are used in drawing these points. This loop should execute number_of_lines times.