In this example, you will learn two ways of calculating LCM (Lowest Common Multiple) of two integers entered by the user (C program to find LCM of two numbers).

C program to calculate LCM

LCM : Lowest Common Multiple of two or more integers is the smallest positive integer that is perfectly divisible by the given integers, without remainder.

For example: LCM of 10 and 20 is 20.

C program to calculate LCM of two numbers

#include <stdio.h>

int main()
{
   int num1, num2, maxValue;

   printf("Enter two numbers: ");
   scanf("%d %d", &num1, &num2);
   //largest integer among num1 and num2 is stored in maxValue
   maxValue = (num1 > num2) ? num1 : num2;

   while(1)  //always true
   {
      if ((maxValue % num1 == 0) && (maxValue % num2 == 0))
      {
         printf("LCM: %d", maxValue);
         break;
      }
      ++maxValue;
   }
   return 0;
}

Output

C program to find LCM of two numbers using GCD

We can also calculate LCM using GCD.
Formula

LCM = (num1 * num2) / GCD

See how to calculate GCD

The above formula can be used to calculate LCM.

#include <stdio.h>
int main()
{
   int num1, num2, i, gcd, lcm;

   printf("Enter two numbers: ");
   scanf("%d %d", &num1, &num2);
   
   //calculation of gcd
   for(i=1; i <= num1 && i <= num2; ++i)
   {
      if(num1 % i == 0 && num2 % i == 0)
         gcd = i;
   }
   //calculation of lcm using gcd
   lcm = (num1 * num2) / gcd;
   printf("LCM: %d", lcm);
  
   return 0;
}

Output