[Tutor] Fahrenheit to Celsius Conversion another problem and Programming Paradigm

[David Rock]

> On Jun 14, 2017, at 09:20, William Gan <ganwilliam at outlook.com> wrote:
> 
> However, today I modified only the print instruction a little to try to print out ℃ (in the second print clause). When I subsequently ran the script all the outputs were executed from the if clause, even when I input other letters (Please see below. I have removed the code to print degree C).
> 
> 
> if unit == 'C' or 'c':
> 
>    f = temp * 9 / 5 + 32
> 
>    print(str(temp) + ' C is equivalent to ' + '%.2f' % f + ' F.')
> 
> elif unit == 'F' or 'f':
> 
>    c = (temp - 32) * 5 / 9
> 
>    print(str(temp) + ' F is equivalent to ' + "%.2f" % c + ' C.')


The problem is your if statement is flawed.

if unit == 'C' or 'c’:

This is not doing what you think it is.  You are expecting:
if unit == ‘C’ or unit == ‘c’

When doing an ‘or’ statement, each part of the logic on each side of the ‘or’ is evaluated, so
if unit == ‘C’ is true, or if ‘c’ is true

is what’s actually being checked.  a bare character, ‘c’ will always evaluate to True, so the if is always true.

What you actually want (checking if unit is ‘C’ or ‘c’) can be done a few ways.  The most common are:

if unit == ‘C’ or unit ==‘c’:

or

if unit in [‘C’, ‘c’]:



> ISSUE 2:
> 
> The second issue relates to the last statement above “I have looked at it many times today and could not see the error”.
> 
> 
> 
> I was hoping that someone, perhaps one with pedagogical experience and knowledge, could advise the following:
> 
> 1.       Is it possible that I may not have the right aptitude or mental paradigm to do computer programming?

Unlikely.  Programming is not about aptitude, it’s more about spending time understanding the rules.  The above is a prime example of getting to understand the rules.  Logic rules are notoriously specific; they check exactly what you tell them to check, which is not always what you think you are asking.  It just takes time.

> 
> 2.       Nevertheless, I intend to keep learning and practicing, but wonder if there is an effective way to get a breakthrough into the programming paradigm? If so, kindly advise how and direct me to a suitable resource to do it.

Really, just keep trying things.  When you run into something like this, the most effective way to troubleshoot is narrow it down to the essential issue.  In this case, “why is the if statement always evaluating to true?”  Look at the parts and re-read what each does (eg, reread how the ‘or’ operator works).

You are doing fine. :-)



—
David Rock
david at graniteweb.com