Shawn Minisall wrote:
> I just learned about if, then elif statements and wrote this program.
> The problem is, it's displaying all of the possibilities even after you
> enter a 0, or if the fat grams are more then the total number of
> calories , that is supposed to stop the program instead of continuing on
> with the print statements that don't apply. Any idea's? thanks
>
> #Prompt for calories
> cal = input("Please enter the number of calories in your food: ")
>
> #Prompt for fat
> fat = input("Please enter the number of fat grams in your food: ")
>
> #Input validation
> if cal or fat <= 0:
> #Display message
> print "Error. The number of calories and/or fat grams must be
> positive"
> print
>
> else:
> #Calculate calories from fat
> calfat = float(fat) * 9
> #Calculate number of calories from fat
> caldel = calfat / cal
>
> #change calcent decimal to percentage
> calcent = caldel * 100
>
> if calfat > cal:
> print "The calories or fat grams were incorrectly entered."
>
> else:
> #evaluate input
> if caldel <= .3:
> print "Your food is low in fat."
> elif caldel >= .3:
> print "Your food is high in fat."
>
> #Display percentage of calories from fat
> print "The percentage of calories from fat in your food is %",
> calcent
>
> Here's an example of the output...
>
> Please enter the number of calories in your food: 50
> Please enter the number of fat grams in your food: 30
> Error. The number of calories and/or fat grams must be positive
>
> Your food is low in fat.
> The percentage of calories from fat in your food is % 0.0
>
> It was supposed to print The calories or fat grams were incorrectly
> entered since the calories from fat was greater then the total number of
> calories.
Boolean problem:
if cal or fat <= 0
That may be the way you say it or "think" it but it won't work.
'cal or fat' is evaluated first. Since they both have values this ALWAYS
evaluates to 1 which is NEVER less than or equal to 0.
You are looking for
if (cal <= 0) or (fat <=0):
(Note: Parenthesis not required, but it may help you understand precedence of
evaluation. Also read here:
http://www.ibiblio.org/g2swap/byteofpython/read/operator-precedence.html
-Larry
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