Question

Ok, so I’m trying to create a program using a while loop to find the greatest common divisor of two numbers. This is what I came up with. However, from what I can tell, the program just seems to skip the loop entirely when I run it. (opers remains 0, divisor always comes back as equal to num1). Anyone out there that can help out a newbie?

/* Define variables for divisors and number of operations */

int num1, num2, divisor, opers;
opers = 0;

/* Prompt user for integers and accept input */

cout << "Please enter two integers with the smaller number first, separated by a space. ";
cout << endl;
cin >> num1 >> num2;

/* Make divisor the smaller of the two numbers */

divisor = num1;

/* While loop to calculate greatest common divisor and number of calculations */

while ( (num1 % divisor != 0 ) && ( num2 % divisor != 0 ) )
{

   divisor--;
   opers++;
}

/* Output results and number of calculations performed */

cout << "The greatest common divisor of " << num1 << " and " << num2 << " is: ";
cout << divisor << endl << "Number of operations performed: " << opers;

Answer 1

As soon as one of those modulo returns non 0, the while loop terminates. (So if any of your inputs immediately results in 0 from the modulo, the loop won’t be entered)

What you probably want:

while ( (num1 % divisor != 0 ) || ( num2 % divisor != 0 ) )
{

   divisor--;
   opers++;
}

This continues the loop until both modulo operations result in 0.