My function for finding LCM does not work. Is there a problem with the while loop?

Question

x = int(input("Enter the first number"))
y = int(input("Enter the second number"))
def calculate_LCM(x,y):
    if (x>y):
        max=x
    else:
        max=y
    while((max%x==0) and (max%y==0)):
        print(max)
        max=max+1
          
          
print(calculate_LCM(x,y))

I was not getting the correct output. aneroid's answer helped me understand the problem with the while loop. — Lotus, Mar 24 '21 at 09:53

score 1 · Answer 1 · answered Mar 23 '21 at 10:06

Your lcm logic is wrong the condition you used in while loop is wrong. LCM logic should be like,

def calculate_LCM(x, y):

   # choose the greater number
   if x > y:
       greater = x
   else:
       greater = y

   while(True):
       if((greater % x == 0) and (greater % y == 0)):
           lcm = greater
           break
       greater += 1

   return lcm

x = int(input("Enter the first number"))
y = int(input("Enter the second number"))

print(calculate_LCM(x,y))

score 1 · Answer 2 · answered Mar 24 '21 at 10:20

Addition to the above answers, you can find LCM of two numbers using GCD. GCD of two numbers take less time when the two numbers are Co prime.First calculate GCD in this way:

def gcd(a,b):
    if b==0:
        return a
    else:
        return gcd(b,a%b)

Then calculate LCM using this formula:

lcm = (a*b)//gcd(a,b)

aneroid · Accepted Answer · 2021-03-23T11:03:16.293

The smallest change to make your code work is to put a not on the while condition - you want the loop to repeat if both remainders are not 0.

while not ((max%x==0) and (max%y==0)):

Btw, your function doesn't return a value, so it implicitly returns None which is what print() receives. Add it after the while-block:

while not (max % x == 0 and max % y == 0):  # remove extra parens and add spaces, PEP8
    max += 1  # same as max = max + 1
return max

Side note: since 0 is boolean-Falsey and non-zero integers and floats are boolean Truthy, that while check can be reduced to:

while max % x or max % y:

so if either value (remainders) is non-zero, the loop repeats.

Tip: max() is a Python built-in so don't use that as a variable name.

My function for finding LCM does not work. Is there a problem with the while loop?

3 Answers3