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This article is created to cover some programs in Java that finds HCF (GCD) and LCM of two numbers entered by user at run-time of the program.

If you're not aware about, how the HCF and LCF of two numbers gets calculated ?

Refer to,
How to Find LCM and How to Find HCF. Now let's move on,
and create the program in Java.

**Note - **HCF stands for Highest Common __Factor__, whereas LCM stands for Least Common __Multiple__.

The question is, *write a Java program to find and print HCF of two numbers. Both the number must be received by user at
run-time.* The program given below is its answer:

import java.util.Scanner; public class CodesCracker { public static void main(String[] args) { int a, b, gcd; Scanner s = new Scanner(System.in); System.out.print("Enter the Two Numbers: "); a = s.nextInt(); b = s.nextInt(); gcd = a; while(true) { if((a%gcd==0) && (b%gcd==0)) break; else gcd--; } System.out.println("\nHCF of Given Two Number = " +gcd); } }

The snapshot given below shows the sample run of above Java program on finding and printing the HCF or GCD of two given
numbers, with user input **18** and **27**

That is,

**Factors of 18 are**1, 2, 3, 6,__9__, 18**Factors of 27 are**1, 3,__9__, 27

Because **9** is the highest common factor between 18 and 27. Therefore HCF is 9.

In above program, I've assumed one number as **gcd** (HCF) of two numbers. And then used a loop that always evaluates to
be **True**, until we got a number that divides both the number.

The above program can also be created in this way. Since, HCF deals with highest common factor. Therefore, we need to
initialize the smaller number to **gcd** initially.

import java.util.Scanner; public class CodesCracker { public static void main(String[] args) { int a, b, hcf; Scanner s = new Scanner(System.in); System.out.print("Enter the Two Numbers: "); a = s.nextInt(); b = s.nextInt(); if(a<b) hcf = a; else hcf = b; while(true) { if((a%hcf==0) && (b%hcf==0)) break; else hcf--; } System.out.println("\nHCF(" +a+ ", " +b+ ") = " +hcf); } }

Here is its sample run with same user input as of previous program's sample run:

The above program can be created in way to use **for** loop, instead of **while**. This program also uses conditional
operator to make the program shorter.

import java.util.Scanner; public class CodesCracker { public static void main(String[] args) { int hcf, a, b; Scanner s = new Scanner(System.in); System.out.print("Enter the Two Numbers: "); a = s.nextInt(); b = s.nextInt(); for(hcf=(a<b)?a:b; true; hcf--) { if((a%hcf==0) && (b%hcf==0)) break; } System.out.println("\nHCF(" +a+ ", " +b+ ") = " +hcf); } }

You'll get the same output as of previous program.

LCM deals with Multiple, the least common multiple. This program find and prints LCM of two given numbers entered by user.

import java.util.Scanner; public class CodesCracker { public static void main(String[] args) { int a, b, hcf, lcm; Scanner s = new Scanner(System.in); System.out.print("Enter the Two Numbers: "); a = s.nextInt(); b = s.nextInt(); if(a>b) lcm = a; else lcm = b; while(true) { if((lcm%a==0) && (lcm%b==0)) break; else lcm++; } System.out.println("\nLCM(" +a+ ", " +b+ ") = " +lcm); } }

Here is its sample run, with again same user input as of previous program:

That is,

**Multiples of 18 are**18, 36,__54__, ...**Multiples of 27 are**27,__54__, ...

Because 54 is the least common multiple of 18 and 27. Therefore LCM is 54.

This program is basically the combined version, as it prints both LCM and HCF (GCD) of any two given numbers.

import java.util.Scanner; public class CodesCracker { public static void main(String[] args) { int x; Scanner s = new Scanner(System.in); System.out.print("Enter the Two Numbers: "); int a = s.nextInt(); int b = s.nextInt(); int numOne = a; int numTwo = b; while(b!=0) { x = b; b = a%b; a = x; } int hcf = a; int lcm = (numOne*numTwo)/hcf; System.out.println("\nHCF(" +numOne+ ", " +numTwo+ ") = " +hcf); System.out.println("LCM(" +numOne+ ", " +numTwo+ ") = " +lcm); } }

The sample run with user input **2** and **5** is shown in the snapshot given below:

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