CODEWITHSUNDEEP
pythonpython-3.x
Incrosnatu Bogdan
Incrosnatu Bogdan

Reputation: 29

What is wrong with my primes number program?

def is_divisible(n, primes):
    for i in range(1, len(primes)):
        if n % primes[i] == 0:
            return True
    return False
primes = []
def find_primes(N):
    for j in range(1, N):
        if is_divisible(j, primes) == False:
            primes.append(j)
        return primes
print(find_primes(200))

It should tell if a number is prime. And just prints 1.

Upvotes: 0

Views: 106

Answers (5)

insertjokes
insertjokes

Reputation: 3

Your return primes line is inside the for loop, which means that it just check the first number (i.e. 1), and returns the result of that single calculation.

Your program should instead return the primes after looking at all the number, not just at the first one.

Upvotes: 0

mlnyc
mlnyc

Reputation: 2726

I think your issue is the indentation of the return statement. Here's your code fixed up:

def is_divisible(n, primes):
    for i in range(0, len(primes)):
        if n % primes[i] == 0:
            return True
    return False

def find_primes(N):
    primes = []
    for j in range(2, N):
        if is_divisible(j, primes) == False:
            primes.append(j)
    return primes

Also avoid globals if you don't have to. find_primes doesnt need to access a global primes list it can declare it locally. Also, notice the range in find_primes that starts at 2 since every number is divisible by 1. Also, indendation matters. In both functions you do not iterate over the entire loop before returning the output (in find_primes) or the default (in is_divisible)

Upvotes: 2

rldrenth
rldrenth

Reputation: 35

In addition to the remark above (your program should start from 2), you do not want to return until you've completed the 'for j in range((2),N): ' loop. That is, you need to dedent the 'return primes' statement.

Upvotes: 0

Tom Ron
Tom Ron

Reputation: 6181

The first number you add is 1, every number is divisible by one and therefore is_divisible(x,1)== True and no number other then 1 is appended to the primes list.

Upvotes: 1

Vincent Ramdhanie
Vincent Ramdhanie

Reputation: 103155

All numbers are divisible by 1. When your program checks if 1 is a prime it determines yes it is so it appends it to the array. Then, when it checks if the next number 2 is divisible by any of the existing primes it says yes, it is divisible by 1 therefore it is not a prime etc etc.

Upvotes: 1

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