Math Interpreter

Python already supports math, whereby you can write code to add, subtract, multiply, or divide values and even variables. But let’s write a program that enables users to do math, even without knowing Python.

In a file called interpreter.py, implement a program that prompts the user for an arithmetic expression and then calculates and outputs the result as a floating-point value formatted to one decimal place. Assume that the user’s input will be formatted as x y z, with one space between x and y and one space between y and z, wherein:

  • x is an integer
  • y is +, -, *, or /
  • z is an integer

For instance, if the user inputs 1 + 1, your program should output 2.0. Assume that, if y is /, then z will not be 0.

Note that, just as python itself is an interpreter for Python, so will your interpreter.py be an interpreter for math!

Hints

Recall that a str comes with quite a few methods, per docs.python.org/3/library/stdtypes.html#string-methods, including split, which separates a str into a list of values, all of which can be assigned to variables at once. For instance, if expression is a str like 1 + 1, then

x, y, z = expression.split(" ")

will assign 1 to x, + to y, and 1 to z.

Demo

Before You Begin

Log into code.cs50.io, click on your terminal window, and execute cd by itself. You should find that your terminal window’s prompt resembles the below:

$

Next execute

mkdir interpreter

to make a folder called interpreter in your codespace.

Then execute

cd interpreter

to change directories into that folder. You should now see your terminal prompt as interpreter/ $. You can now execute

code interpreter.py

to make a file called interpreter.py where you’ll write your program.

How to Test

Here’s how to test your code manually:

  • Run your program with python interpreter.py. Type 1 + 1 and press Enter. Your program should output:
    2.0 
    
  • Run your program with python interpreter.py. Type 2 - 3 and press Enter. Your program should output:
    -1.0
    
  • Run your program with python interpreter.py. Type 2 * 2 and press Enter. Your program should output
    4.0
    
  • Run your program with python interpreter.py. Type 50 / 5 and press Enter. Your program should output
    10.0
    

You can execute the below to check your code using check50, a program that CS50 will use to test your code when you submit. But be sure to test it yourself as well!

check50 cs50/problems/2022/python/interpreter

Green smilies mean your program has passed a test! Red frownies will indicate your program output something unexpected. Visit the URL that check50 outputs to see the input check50 handed to your program, what output it expected, and what output your program actually gave.

How to Submit

In your terminal, execute the below to submit your work.

submit50 cs50/problems/2022/python/interpreter