C Exercises: Determine the LCM of two numbers using HCF

Last update on March 18 2025 13:35:29 (UTC/GMT +8 hours)

44. LCM Using HCF

Write a C program to find the LCM of any two numbers using HCF.

The task is to write a C program that calculates the Least Common Multiple (LCM) of two given numbers using their Highest Common Factor (HCF). The program should implement the relationship between LCM and HCF, given by the formula: LCM(a, b) = (a * b) / HCF(a, b).

Visual Presentation:

Determine the LCM of two numbers using HCF

Sample Solution:

C Code:

#include <stdio.h> // Include the standard input/output header file.

void main()  
{  
    int i, n1, n2, j, hcf = 1, lcm; // Declare variables to store input and results.

    printf("\n\n  LCM of two numbers:\n "); // Print a message.
    printf("----------------------\n"); // Print a separator.

    printf("Input 1st number for LCM: ");  // Prompt the user for input.
    scanf("%d", &n1);  // Read the first number from the user.
    printf("Input 2nd number for LCM: ");  // Prompt the user for input.
    scanf("%d", &n2);  // Read the second number from the user.

    j = (n1 < n2) ? n1 : n2;  // Determine the smaller of the two numbers. 

    // Loop to find the highest common factor (HCF).
    for(i = 1; i <= j; i++)  
    {  
        if(n1 % i == 0 && n2 % i == 0)  
        {  
            hcf = i;  // Update the HCF whenever a common factor is found.
        }  
    }  

    // Calculate the least common multiple (LCM).
    lcm = (n1 * n2) / hcf;

    // Print the result.
    printf("\nThe LCM of %d and %d is : %d\n\n", n1, n2, lcm);  

}

Output:

  LCM of two numbers:                                                                                         
 ----------------------                                                                                       
Input 1st number for LCM: 15                                                                                  
Input 2nd number for LCM: 20                                                                                  
                                                                                                              
The LCM of 15 and 20 is : 60

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to compute the LCM of two numbers using the formula LCM = (a*b)/HCF.
Write a C program to calculate the LCM of two numbers recursively using the Euclidean algorithm for HCF.
Write a C program to find the LCM of two numbers and then verify it by listing several common multiples.
Write a C program to compute the LCM of two numbers and check whether it is even or odd.

C Programming Code Editor:

Previous: Write a C program to find HCF (Highest Common Factor) of two numbers.
Next: Write a program in C to find LCM of any two numbers.