Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Chris Warrick <kwpolska@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Creating a calculator
Date: Fri, 1 Jul 2016 10:57:11 +0200
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On 1 July 2016 at 05:08, Elizabeth Weiss <cake240@gmail.com> wrote:
> while True:
>         print("Options:")
>         print("Enter 'add' to add two numbers")
>         print("Enter 'subtract' to subtract two numbers")
>         print("Enter 'multiply' to multiply two numbers")
>         print("Enter 'divide' to divide two numbers")
>         print("Enter 'quit' to end the program")
>         user_input=3Dinput(":")
>         if user_input=3D=3D"quit":
>                 break
>         elif user_input=3D=3D"add":
>                 num1=3Dfloat(input("Enter a number"))
>                 num2=3Dfloat(input("Enter another number"))
>                 result=3Dstr(num1+num2)
>                 print("The answer is"+ result)
>         elif user_input=3D=3D"subtract":
>                 num1=3Dfloat(input("Enter a number"))
>                 num2=3Dfloat(input("Enter another number"))
>                 result=3Dstr(num1-num2)
>                 print("The answer is"+result)
>
> Two questions:
> 1. Why do I need to put ' ' around the words add, subtract, multiply, qui=
t, etc. when it is already in quotes in print()? When the calculator asks m=
e which option I would like to choose I do not write 'add'- I only write ad=
d.

This is used for display. The single quotes will be displayed as part
of the string. This is so that people notice the commands, for
example.

>>> print("Enter 'add' to add two numbers")
Enter 'add' to add two numbers
>>> print("Enter add to add two numbers")
Enter add to add two numbers
>>> print('Enter "add" to add two numbers')
Enter "add" to add two numbers

> 2. The program I am using to help me learn python mentions that the outpu=
t line could be put outside the if statements to omit repetition of code. W=
hat does this mean and how would I write the code differently according to =
this?

Look at your current code. The following three lines appear twice (and
will appear 4 times if you add multiplication and division):

> num1=3Dfloat(input("Enter a number"))
> num2=3Dfloat(input("Enter another number"))
> print("The answer is"+ result)

This is code repetition. It=E2=80=99s discouraged, because if you have 4
copies of a longer segment, and you want to change something, you
would have to remember to change it in 4 places. In this case, you can
avoid code reuse like this:

1. Check if user said 'quit', and if yes, break from the loop. (Ignore
invalid input for now)
2. Ask the user for two numbers.
3. Make an if/elif/else structure to calculate the result.
4. Print out the result outside of `if`.

Example for 3. and 4.:
if user_input =3D=3D 'add':
    result =3D num1 + num2  # no need to call str() if you use commas in pr=
int()
elif user_input =3D=3D 'subtract':
    result =3D num1 - num2
# other elif clauses go here
print("The result is", result)

--=20
Chris Warrick <https://chriswarrick.com/>
PGP: 5EAAEA16