Python While Loop To Find Prime Does Not Terminate

Question

flag = 0
n = int(input('\nEnter whole number to check : '))
i = 2
while i <= (n/2):
    if (n%i) == 0:
        flag = 1
        break
if n == 1:
    print('1 is neither prime nor composite')
elif flag == 0:
    print(n,' is a prime number.')
elif flag == 1:
    print(n,' is not a prime number.')

Upon Entering a number >= 3, the program stalls and the cursor keeps blinking endlessly. I initially tries 277, then 13, then 5, then 3 - none of which gave a result even after a minute.

Entering 2 worked.

There must be something wrong with the code.

Answer 1

Your loop is not changing n or i, which are the conditions on which it stops.

I think the correct code should be:

flag = 0
n = int(input('\nEnter whole number to check : '))
i = 2
while i <= (n/2):
    if (n%i) == 0:
        flag = 1
        break
    i += 1
if n == 1:
    print('1 is neither prime nor composite')
elif flag == 0:
    print(n,' is a prime number.')
elif flag == 1:
    print(n,' is not a prime number.')