CODEWITHSUNDEEP
pythonfor-loopwhile-loop
Mathew E.
Mathew E.

Reputation: 77

Python: Find Prime Number Algorithm

Recently I was given a challenge to my coding skills by my teacher since he saw that I was already knowledgeable in what he was teaching. The question is as follows.

Create a program that prompts the user for 2 numbers. The program will then display all the prime numbers in between the two given numbers, including the given numbers. Note: You cannot assume the first input is bigger than the second input.

So I took this question and built a fairly simple algorithm and ran it and it worked. I opened it today to find out for some reason my output is occasionally wrong, for example when you input 8 and 29 I get 27. I am looking for HINTS as to what is wrong with my logic because I cannot for the life of me figure out what Im doing wrong. I dont want straight up fixes because I would like to learn as much from this and doing it as much as possible by myself.

numbers = [int(input("First Number")), int(input("Second Number"))]
numbers.sort()

numList = []
#Removing Even Numbers
for num in range(numbers[0],numbers[1] + 1):
    if num % 2 != 0:
        numList.append(num)

#Checking For Prime Numbers
for currNum in numList:
   #Set Start number to divide
    i = 2
    while i < currNum:
        #Checks if the currNum can be divisble by i and is a whole number
        if currNum % i != 0:
          i = i + 1
        else :
          numList.remove(currNum)
          break

print(numList)

From what I have learned from testing this out it seems like 27 is never checked during my for loop or while loop even though it is in the numList array.

Upvotes: 1

Views: 169

Answers (1)

Daniel
Daniel

Reputation: 42758

Never remove items form a list you are iterating over. Instead create a new list:

numbers = [int(input("First Number")), int(input("Second Number"))]
numbers.sort()

primes = []
for num in range(numbers[0], numbers[1] + 1):
    #Set Start number to divide
    i = 2
    while i < num:
        #Checks if the currNum can be divisble by i and is a whole number
        if num % i == 0:
            break
        i += 1
    else:
        primes.append(num)

print(primes)

Upvotes: 2

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