How to calculate greatest common divisor and least common multiple in C++

Menu driven program to find out the Greatest Common Divisor and Least Common Multiple of two numbers

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#include<iostream>

#include<conio.h>

using namespace std;

int gcd(int first_number, int second_number);

int lcm(int first_number, int second_number);

int main()

{

int first_number = 0, second_number = 0, gc_number = 0, lc_number = 0, choice = 0;

       cout << "\n\n\t\tGreatest Common Divisor OR Least Common Factor";

       cout << "\n\n\t\t\t  1. GCD (2 Numbers)\n\n\t\t\t  2. LCM (2 Numbers)";
       
       cout << "\n\n\t\t\t  3. Exit";

       cout << "\n\n\n\n\t\tEnter your choice  ->  ";

       cin >> choice;

       switch(choice)

       {

              case 1:

                     cout << "\n\n  First Number  -  ";

                     cin >> first_number;

                     cout << "\n\n  Second Number -  ";

                     cin >> second_number;

                    

                     gc_number = gcd(first_number, second_number);

                     cout << "\n\n  Greatest Common Divisor of " << first_number;
                     
                     cout << " and " << second_number << " is " << gc_number;

                     break;

              case 2:

                     cout << "\n\n  First Number  -  ";

                     cin >> first_number;

                     cout << "\n\n  Second Number -  ";

                     cin >> second_number;

                     lc_number = lcm(first_number, second_number);

                      
                     cout << "\n\n  Least Common Multiple of " << first_number;
                     cout << " and " << second_number << " is " << lc_number;

                    

                     break;

              case 3: exit(1);

                     break;

              default: cout << "\n\n\t Inputted Choice is Wrong";

       }

       getch();

       return 0;

}

int gcd(int first_number, int second_number)

{

  int result = 0, counter = 0, smaller = 0;

  if (first_number < second_number)

  {

       smaller = first_number;

  }

  else

  {

       smaller = second_number;

  }

  for(counter = 1; counter <= smaller; counter++)

  {

    if (((first_number % counter) == 0 ) && ((second_number % counter) == 0))

    {

        result = counter;

    }

  }

  return result;

}

int lcm(int first_number, int second_number)

{

  int result = 0, counter = 0;

  for(counter = 1; counter <= first_number * second_number; counter++)

  {

     if (((counter % first_number) == 0) && (((counter % second_number) == 0)))

     {

           result = counter;

           break;

     }

  }

     return result;

}

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Check out the links for the logics -

• Greatest Common Divisor
• Least Common Factor