CS 150 - Assignment 4 - Math Whiz

Due: Wednesday 3/15 at the beginning of class

***** Extended until Thu 3/16 at 9:00am *****

For this assignment, you are going to be implementing a timed game where the user answers as many simple math questions as possible in a given time period.

Generating random equations

Before you start working, make sure that you understand at a high-level how the game is supposed to be played. The prelab contains instructions on how to run a working version. We're going to build up the final version of this program one piece at a time. As you build each piece, make sure you understand where it fits into the larger program and make sure it's working correctly before moving on. The first thing we'll need is the ability to generate a random equation. Our random equations will contain the operators +, -, and *. The following pseudocode describes one way to generate a random equation. (Pseudocode is a way to describe an algorithm in detail without getting bogged down in language specifics. It is a compromise between English and code.) Using this approach, we can generate a random equation with as many operators as we would like.

Write a function called random_equation that takes as input a single parameter, the number of operators to generate in the random equation, and returns a string representing a random math equation involving the numbers 1-10 and operators +, -, *. Here are a few example runs:

>>> random_equation(4)
'5 - 6 - 7 * 6 * 4'
>>> random_equation(1)
'3 * 7'
>>> random_equation(2)
'8 - 5 * 2'
>>> random_equation(7)
'8 + 7 + 4 - 7 - 2 * 3 * 2 * 4'
Hints: You'll likely need to use some sort of loop structure to get the repetition (i.e., for or while). Think about which one is more appropriate here. Also, notice that our equation is a string, so we'll be building up a string similar to how we did in the last assignment by appending on new pieces.

Getting an answer

Now that we have an equation, we need to have some way of repeatedly prompting the user for an answer until that answer is correct. Before writing any more code, read through this whole section since I give some hints/advice at the end.

There is a function called eval built into Python that evaluates any expression represented as a string and returns the value represented by that expression. We're going to use this function to figure out what the answer is to our random equation. For example:

>>> eq = random_equation(4)
>>> eq
'7 * 5 - 2 - 4 * 8'
>>> x = eval(eq)
>>> x
Notice that the value that eval returns is an int, which we would expect. If you're curious, eval can be used to evaluate more complicated string expressions that include function calls, etc.

Write a function called query_equation that takes as a parameter a string representing an equation (e.g., what is returned from your random_equation function). This function should prompt the user with the equation and then wait for an answer from the user. If the user gets it wrong, then it will output a message to the user indicating this and then prompt the user again with the equation (eval will be useful in figuring out if the user's answer is correct). The function should continue to prompt the user until they get the equation right. When the user does finally get it right, the function should print "Correct!". The message the user gets if they answer incorrectly should depend on how close there are:

There are many ways you can tackle this function, but I suggest an incremental approach:
  1. Write the function without a loop so that it only queries the user once and then either prints out "Correct" or "Incorrect" depending on whether or not the user got it right. Remember that input returns a string, so if you want a number you need to convert it to one!
  2. Add some sort of loop to repeatedly query the user when incorrect.
  3. Add in "Close. Try again." that is printed when the user gets it wrong but is within 2 of the correct answer.
Here is a quick example with query_equation:
>>> eq = random_equation(2)
>>> eq
'5 + 9 + 7'
>>> query_equation(eq)
5 + 9 + 7 = 25
Keep trying!
5 + 9 + 7 = 22
Close. Try again.
5 + 9 + 7 = 20
Close. Try again.
5 + 9 + 7 = 21

Playing the game

We now have all of the pieces we need to put together our final program. Write a function called play_game that takes a single parameter, the game duration in seconds. The function should use the time function in the time module to time the user. As long as the elapsed time hasn't gone over the input game duration, you should present the user with a random equation and then keep track of how many they get correct (you should be thinking about some kind of loop structure). When time runs out, you should print out how many the user got correct and how long the game was played for.

This function should NOT be a lot of code, but should utilize the two previous functions that you've written. The key responsibility of this function is timing and keeping track of how many it got correct. Recall from the prelab that we can measure how much time has elapsed by first recording a starting time and then measuring the difference between the current time returned by time() and the initial start time.

As with the previous function, I would suggest an incremental approach. There are many ways you could tackle this, but one would be:

  1. Start by getting the timing loop working. For example, just get any input from the user (using input) and then print it out. Do this over and over again until the time has elapsed.
  2. Change your loop now to generate a random equation and then use that equation to query the user.
  3. Finally, add in the bookkeeping part where you keep track of how many the user got right and then at the end, print out the game summary.
NOTE: because we are doing the timing outside of the query_equation function, time will NOT expire until the user gets the answer right. This is fine and how I expect yours to work.

The finishing touches

When your play_game function is working, you can finish things up: Complete your program by adding some statements at the end of your file to play the game automatically when your program is run. You should ask the user if they want to play a game. If they say "yes", then you should prompt the user to see how long they want to play for (in seconds) and then the game should start. If the user does not say "yes", just give the user a nice goodbye message. All of this code should be outside of your play_game function.

Extra Points

You may earn up to 2 extra points on this assignment by adding improvements to your program. If you do, include in your comments at the top of your program what you added. Below are some suggestions, but feel free to add you own:

When you're done

Make sure that your program is properly commented: In addition, make sure that you've used good style.

What to hand in:

You should have implemented: Submission procedure: Submit your .py file online using the digital submission link on the course web page. You must have submitted it online before the beginning of class on Wednesday.


    correctly formed equations 3
    all 3 operators randomly 1
    number varies based on input 1
    print correct/incorrect correctly 1
    loops until correct 3
    close answers get different feedback 1
    generates random equation and queries user 1
    loops until time expired 3
    prints out game summary 1
Final gaming code
    correctly handles user input for game starting 1
    gets game duration 1
Prelab 3
Comments, style 3
Extra points 2
Total 23 + 2