Matty Sarro wrote:
Hey Everyone,
I'm currently trying to work through MIT's opencourseware and am using
python. The second assignment they offer is to determine the 1000th prime
number. Below is the code I am using:
#Assignment 1a
#Determine the 1000th prime number
candidate=3
#Already know that 2 is prime
primeCount=1
while (primeCount<=1000):
for i in range (2,candidate):
if ((candidate%i)==0):
print(candidate, " is not a prime")
else:
print(candidate, " is a prime!")
primeCount+=1
candidate+=2
Now I'm not looking for a solution, but I'm hoping that someone can at least
tell me where the error in my logic is.
The outer loop keeps count and will keep iterating until the 1000th prime
number has been found.
The inner loop just attempts to divide the candidate number by each possible
factor until it's reached, and then increases the candidate number value by
two since even numbers above 2 aren't prime.
The if statement inside the inner loop simply checks if there is a remainder
when attempting to divide the candidate by the possible factor. If there
isn't, its a factor and we can print "not a prime". If there is always a
remainder, nothing is a factor and so the candidate is a prime.
I figured it seemed simple enough, but I keep getting a massive output and
almost nothing listed is a correct prime number.
Please be gentle, its my first post and I haven't programmed in ages :)
-Matty
Once you discover a particular value is not a prime, you need to get out
of that for loop. Add a break after the appropriate print.
Also, the print that says it IS a prime is misplaced. You only know
that if you've gone all the way through the loop without ever hitting
the break. That's a candidate for the 'else' clause of the for loop.
There are other changes you could make for efficiency, but get it
working correctly first.
DaveA
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