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C Program to Find LCM of two Numbers

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This tutorial will teach you how to find the LCM (Least Common Multiple) of two numbers in C. To understand this example, you should have knowledge of the following C programming topics.

The LCM (Least Common Multiple) of two integers is the smallest positive integer that is perfectly divisible by both the numbers  (without a remainder). For example, the LCM of 30 and 40 is 120.

Find LCM in C using loop

#include <stdio.h>

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

  printf("Enter 2 positive integers:\n");
  scanf("%d %d", &num1, &num2);
  
  //the largest among these two is stored in largest
  largest = (num1 > num2) ? num1 : num2;

  while (1)  //always true
  {
    if (largest % num1 == 0 && largest % num2 == 0)
    {
      printf("The LCM of %d and %d is: %d", num1, num2, largest);
      break;
    }

    ++largest;
  }

  return 0;
}

Output:

Enter 2 positive integers:
30
40
The LCM of 30 and 40 is: 120

C Program to Find LCM using GCD

#include <stdio.h>

int main()
{
  int num1, num2, i, gcd, lcm;

  printf("Enter 2 positive integers:\n");
  scanf("%d %d", &num1, &num2);

  for (i = 1; i <= num1 && i <= num2; ++i)
  {
    // check if i is a factor of both integers
    if (num1 % i == 0 && num2 % i == 0)
      gcd = i;
  }

  lcm = (num1 *num2) / gcd;   //use of gcd

  printf("The LCM of %d and %d: %d", num1, num2, lcm);
  return 0;
}

Output:

Enter 2 positive integers:
30
40
The LCM of 30 and 40: 120

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