CPSC 120 B

Lab 6: Repetition

As usual, create a directory to hold today's files. All programs that you write today should be stored in this directory.

$ cd ~/cs120/labs
$ mkdir lab6 
$ cd lab6

Practice Problem #1

Write a python program that prints all of the numbers between 25 and 50. Your code for this program should be no longer than 5 lines long.

Example

$ python3 practice1.py
25
26
27
... omitted for space ...
49
50

Practice Problem #2

Write a python program that prints all multiples of 7 less than 100. Your code for this program should be no longer than 5 lines long.

Example

$ python3 practice2.py
7
14
21
... omitted for space ...
91
98

Polygon

A convex regular polygon is a shape that consists of a sequence of straight lines that all have the same length and meet at the same angle. Convex regular polygons can be parameterized according to the number of sides the shape has. For example, the convex regular polygons with 3, 4, and 5 sides are an equilateral triangle, a square, and a pentagon. As the number of sides increases the names of the polygons get more complicated, for example a 36-sided convex regular polygon is called a triacontakaihexagon. In this activity you will create a function that can create any convex regular polygon.

Details

In Emacs, create a Python program in a filed called polygon.py that uses turtle graphics to draw a convex regular polygon. It should prompt the user for the number of sides and for the circumference of the polygon it draws.

Test your program by running it multiple times with different input values. Make sure your code follows the courses code conventions.

Example

$ python3 polygon.py
Enter the number of sides: 5
Enter the circumference: 100

$ python3 polygon.py
Enter the number of sides: 6
Enter the circumference: 200

Hint

Drawing a convex regular polygon is a lot like drawing a star, the turtle should repeatedly move forward and turn.
Unlike the star, you will need to use a for loop to draw the polygon. Because the program must work for any number of sides, the number of times the turtle moves forward and turns will be different each time the program is run. Use the number of sides entered by the user, don't forget to make it an int, to control the number of times the loop runs.
Also just like drawing the star, the turtle will need to turn once for each corner of the polygon of the star. So you can calculate how much it should turn because the sum of all of the turns will total 360°.
Calculate the distance the turtle moves forward from the circumference of the polygon. The turtle will move forward the same distance every time, so the sum of every forward movement must be the circumference of the polygon.

Challenge

As the number of sides in a convex regular polygon approaches infinity, it becomes a circle. Write a program that takes advantage of this to draw a circle. The program should prompt the user for the circumference of the circle. Note that at some point adding more edges to a polygon approximating a circle does not produce a better looking circle, so the number of edges depends on the size of the circle. The program should calculate the number of edges needed to draw a good looking circle assuming that if all edges are 2 units long, the circle will look good.

Spiral

The human visual system did not evolve to percieve the types of regular patterns that are simple to create with programming. A spiral of contrasting colors can produce the illusion of motion when you move your eyes over the static image.

Details

In Emacs, create a Python program in a file called spiral.py that uses turtle graphics to draw a square spiral. The spiral can be any size, but it looks cooler if it is bigger with little distance between each layer of the spiral. Make sure your code follows the courses code conventions.

Example

$ python3 spiral.py

Hint

To draw the square spiral the turtle should repeatedly move forward and turn. So you should use a loop.
The turtle should always turn 90°.
The distance forward the turtle moves should increase with every iteration of the loop. The loop variable increases with every iteration of the loop, so you can use the loop variable to compute the forward distance.

Challenge

Create a circular spiral like the following: