C program to find LCM of two numbers

Write a C program to input two numbers from user and find LCM (Lowest Common Multiple) using loop. How to find LCM of two given numbers in C programming. Logic to find LCM of two number in C program.



Input number1: 12
Input number2: 30


LCM = 60

Required knowledge

Basic C programming, Conditional operator, If else, While loop, Infinite while loop

What is LCM?

LCM is a smallest positive integer that exactly divides two or more numbers. For Example

LCM (Least Common Multiple)

Logic to find LCM of two numbers

Step by step descriptive logic to find LCM of two numbers.

  1. Input two numbers from user. Store them in some variable say num1 and num2.
  2. Find maximum between two numbers. Store the result in some variable, say max. Maximum is used to generate next multiple which must be common to both.
  3. If max is exactly divisible by both numbers. Then you got your answer, store max to some variable say lcm = max. If LCM is found then terminate from loop using break keyword.
  4. If max is not divisible by both numbers. Then generate next multiple of max.
  5. Repeat steps 2 to 3 step till LCM is found.

Program to find LCM of two numbers

 * C program to find LCM of any two numbers

#include <stdio.h>

int main()
    int i, num1, num2, max, lcm=1;

    /* Input two numbers from user */
    printf("Enter any two numbers to find LCM: ");
    scanf("%d%d", &num1, &num2);

    /* Find maximum between num1 and num2 */
    max = (num1 > num2) ? num1 : num2;

    /* First multiple to be checked */
    i = max;
    /* Run loop indefinitely till LCM is found */
        if(i%num1==0 && i%num2==0)
             * If 'i' divides both 'num1' and 'num2'
             * then 'i' is the LCM.
            lcm = i;

            /* Terminate the loop after LCM is found */

         * If LCM is not found then generate next 
         * multiple of max between both numbers
        i += max;

    printf("LCM of %d and %d = %d", num1, num2, lcm);

    return 0;

Let us take a note of above program.

  • while(1) is an infinite loop that runs indefinitely until LCM is found.
  • Do not confuse with the statement max = (num1 > num2) ? num1 : num2;. It is used to find maximum between two numbers.

Move a step forward and learn to find LCM using recursive approach.

Must learn – Program to find LCM using recursion.


Enter any two numbers to find LCM: 12
LCM of 12 and 30 = 60

Happy coding 😉