Why can two sets of the same code produce two different outputs?

Question

I'm making code that can determine whether the number entered by the user is prime or not. But I kept running into a bug that oddly enough, my friend's code didn't, even though our codes was the same down to the letter.

#my friend's
num = int(input())

if num > 1:
   for i in range(2,num):
       if (num % i) == 0:
           print(num,"is not a prime number")
           print(i,"times",num//i,"is",num)
           break
   else:
       print(num,"is a prime number")
else:
   print(num,"is not a prime number")

#mine
num = int(input())

if num > 1:
    for i in range(2,num):
        if (num % i) == 0:
            print(num,"is not a prime number")
            print(i,"times",num//i,"is",num)
            break
        else:
            print(num,"is a prime number")
else:
    print(num,"is not a prime number")

If I enter 121 to my friend's code, the output will be:

121
121 is not a prime number
11 times 11 is 121

But if I enter 121 to my code, the output will be:

121
121 is a prime number
121 is a prime number
121 is a prime number
121 is a prime number
121 is a prime number
121 is a prime number
121 is a prime number
121 is a prime number
121 is a prime number
121 is not a prime number
11 times 11 is 121

What's wrong with mine?

Did you manage to understand the difference in the code? – Firefighting Physicist Dec 07 '22 at 06:32 — Firefighting Physicist, Dec 07 '22 at 06:32
@FirefightingPhysicist yes, I did! – najma Dec 13 '22 at 05:40 — najma, Dec 13 '22 at 05:40

Firefighting Physicist · Answer 1 · 2022-12-05T06:55:10.070

0

Look at your indentation. Your friends code does for or else, your code does if or else. Read more about why else can be used with for here.

#your friend's
...
   for i in range(2,num): 
       if ...
   else: # enters when `for` loop breaks
       ...
   
#you
...
    for i in range(2,num):
        if (num % i) == 0:
            ...
        else: # enters when `if` returns false
            ...

edited Dec 05 '22 at 06:55

answered Dec 05 '22 at 06:48

Firefighting Physicist

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score 0 · Answer 2 · answered Dec 05 '22 at 07:01

There is indentation issue with your code.

#my friend's
num = int(input())

if num > 1:
   for i in range(2,num):
       if (num % i) == 0:
           print(num,"is not a prime number")
           print(i,"times",num//i,"is",num)
           break
       else:
           print(num,"is a prime number")
else:
   print(num,"is not a prime number")

Here i

#mine
num = int(input())

if num > 1:
    for i in range(2,num):
        if (num % i) == 0:
            print(num,"is not a prime number")
            print(i,"times",num//i,"is",num)
            break
        else:
            print(num,"is a prime number")
else:
    print(num,"is not a prime number")

Why can two sets of the same code produce two different outputs?

2 Answers2