My backwards logic
gordon at panix.com
Fri Sep 5 19:08:05 CEST 2014
In <1enj0att6bkrnvb81rhma5dbuk3h28agl8 at 4ax.com> Seymore4Head <Seymore4Head at Hotmail.invalid> writes:
> I'm still doing practice problems. I haven't heard from the library
> on any of the books I have requested.
> This is not a hard problem, but it got me to thinking a little. A
> prime number will divide by one and itself. When setting up this
> loop, if I start at 2 instead of 1, that automatically excludes one of
> the factors. Then, by default, Python goes "to" the chosen count and
> not "through" the count, so just the syntax causes Python to rule out
> the other factor (the number itself).
> So this works:
> while True:
> print (a)
> for x in range(2,a):
> if a%x==0:
> print ("Number is not prime")
> wait = input (" "*40 + "Wait")
> But, what this instructions want printed is "This is a prime number"
> So how to I use this code logic NOT print (not prime) and have the
> logic print "This number is prime"
There are two basic tactics you can use:
1. Initialize an "isprime" flag to True at the top of the while loop.
In the for loop, replace the print statement with a statement that
sets isprime to False. After the for loop, insert a check on isprime,
and print "This number is prime" if isprime is still True.
2. Create a separate function just for testing if a number is prime, which
returns True or False. Then call that function within your while loop.
John Gordon Imagine what it must be like for a real medical doctor to
gordon at panix.com watch 'House', or a real serial killer to watch 'Dexter'.
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