COMP 141 Fall 2016

Program 4: Geometry

Assigned:Friday, September 23
Due: Sunday, October 2, 2016 by 11:55pm

For this assignment, you will write a program that allows the user to compute measurements of various geometric shapes using a menu-driven interface. This assignment is meant to test your ability to define and call functions properly, and it will also incorporate conditional statements (if-elif-else) as well as a simple while loop.

About functions

Now that we are beginning to write longer programs, we will practice dividing our programs into functions. This is a critical habit to develop, because building a program out of functions that work together enables faster software development, because functions can be tested individually, then combined together into larger functions.

When first thinking about a program, try to envision it as a set of components that all fit together like a puzzle, where each component handles a separate, distinct task. Consider making separate tasks into separate functions. Now this idea can be taken to the extreme, which is not helpful, as using too many functions, especially if these functions all need access to the same variables, ends up being very messy because you have to write functions that take, for instance, ten arguments. Try to find a balance between too many functions and too few.

What you need to do

First, write five functions that compute and return the following:

Area of a circle. This function takes one parameter, the radius.
Area of a rectangle. This function takes two parameters, the length and width.
Area of a square. This function takes one parameter, the length of a side. However, because a square is just a special type of rectangle (where the sides have the same length), have this function call your area of a rectangle function to compute the answer. In other words, do not directly compute the area of a square inside this function, instead, call your area of a rectangle function with appropriate arguments and return the value that comes back.
This idea, while probably taken a little too far in this case, is normally good programming practice: We are using an already-solved problem to solve a new problem. Here, a square is just a special case of a rectangle, so use the solution for a rectangle we've already written rather than writing a completely new solution.
Area of a triangle. This function takes two parameters, the base and height.
The surface area of a rectangular prism. This function takes three parameters, the length, width, and height.
Note that the surface area of this shape can be computed as the sum of the areas of the six faces of the prism. Because each face is a rectangle, call your area of a rectangle function to write this function. You will need to call it three times.
Again, I know I'm taking the idea of reusing functions to the extreme, but I want you to practice calling functions and capturing return values.

If you write these functions correctly, none of them should contain input statements or print statements. Each one interacts with outside functions only through parameters and return values.

Second, write your main() function to do this:

The user is first asked what kind of shape they want to calculate the area (or surface area) of.
The user will type in the name of the shape as a string (e.g., circle, rectangle, square, triangle, or prism).
Use if-elif-else statements to figure out what shape they wanted, then ask the user to type in the appropriate attributes of the shape (e.g., for circle you would ask for the area, for square you would ask for the length of a side). If the user types in an invalid shape name, then print an appropriate error message.
Display the area of the shape, followed by a message asking the user if they want to calculate the area of another shape. If they answer yes, then run the program again. You should use a while loop for this part.

You may assume the user will type in the name of the shape either in all lowercase, or with a capital first letter (i.e., your program should work correctly for both "triangle" and "Triangle"). You do not have to handle any other type of capitalization. If the user types in an invalid shape name (like "TrIaNgLe" or "trapezoid"), your program should print an appropriate error message.

Testing your program

You should test your program thoroughly to make sure all of your shape functions work. You may assume the user will never give "bad" input --- the user will always type in integers for the numbers, and never negative numbers or zero.

Sample interaction

Note that this is only a sample. Your program should work with any order of shapes the user wants.

What shape do you want? triangle
What is the base? 3
What is the height? 4
The area of the triangle is 6.0
Do you want to calculate another area? (yes or no) yes

What shape do you want? Square
What is the side length? 7
The area of the square is 49
Do you want to calculate another area? (yes or no) yes

What shape do you want? rectangle
What is the length? 8
What is the width? 5
The area of the rectangle is 40
Do you want to calculate another area? (yes or no) yes

What shape do you want? prism
What is the length? 6
What is the width? 5
What is the height? 4
The surface area of the prism is 148
Do you want to calculate another area? (yes or no) yes

What shape do you want? Hexagon
I don't know that shape.
Do you want to calculate another area? (yes or no) yes

What shape do you want? square
What is the side length? 5
The area of the square is 25
Do you want to calculate another area? (yes or no) yes

What shape do you want? Triangle
What is the base? 9
What is the height? 8
The area of the triangle is 36.0
Do you want to calculate another area? (yes or no) yes

What shape do you want? Circle
What is the radius? 6
The area of the circle is 113.03999999999999
Do you want to calculate another area? (yes or no) no

Comments in your code

Because I'm requiring you to write functions in this assignment, I'm adding additional mandatory comments. It is good practice to always describe your functions in terms of what they do, the input they take in and the output they produce.

For every function you write (except main), you must include a comment immediately before the function definition line that contains:

A description of what the function does.
Any parameters the function takes (if any), along with their meanings.
The return value of the function, if there is one, and what it means.

Here's an example you'd use for a function that computes the circumference of a circle:

	# This function computes the circumference of a circle.
	# Parameters: r, the radius of the circle.
	# Returns: the circumference of the circle.
	def circumference_of_circle(r):
	  return 2 * math.pi * r

What to Do

Create a Python program named yourlastname_yourfirstname_prg4.py

Include the standard program header at the top of your Python file.

Follow the comment guide to correctly comment your code.

Submit your Python file on Moodle under Program 4.

Requirements

A good program will do all of the following:

Program file is named correctly.

Include the standard program header as a comment at the top of your program.

Include six functions in total (main and five others).

Include all user prompts for information in the main function.

Output to the user the area of each shape they input.

Correctly use a while loop to allow the user to keep calculating shape areas for as long as they like.

Code is commented appropriately including function comments, is neatly and clearly formatted, and it includes proper use of 'white space'.

Hints

Write your five geometric functions first. Test them using the Python shell before you write the main function.
Write your main function first without a while loop (so it will only run once). Make sure it works fine for a single shape, then put the while loop in.

Challenge Problems

Do not work on these until you have completely solved the basic assignment.

Add a menu to the program so the user can type in a number for their shape rather than the word. For example, you could print a menu showing "(1) Circle (2) Rectangle... (6) Quit." Change the while loop so the user can use the menu to quit, rather than having to ask the question about whether they want to calculate another shape.
Enhance your program using the graphics library. Make it so the user will not specify the shapes in terms of lengths or widths or radii, but rather by the (x, y) endpoints of the shapes. Once the user picks a shape and endpoints, the shape will be drawn on the screen, as well as the area calculated.
Make it so the endpoints of the shapes can be specified by clicking the mouse on the canvas, rather than typing them in at the keyboard.

Grading

Your program will be graded on correctness, as well as on coding style, which refers to choices you make when writing your code, such as good use of variable names, appropriate indentation, and comments (this is not an exhaustive list). See the syllabus for further grading details.

You will receive one bonus point for every complete day your program is turned in early, up to a maximum of five points. For instance, if your program is due on September 20 at 11:59pm, if you turn in your code on Moodle any time on September 19 from 12:00am through 11:59pm, you will receive one extra point on your project. Programs submitted on September 18 from 12:00am through 11:59pm will receive two points. This pattern continues for up to five points.