Help with Greatest Common Divisor

[Wordz91]

I'm supposed make a program that finds the greatest common divisor between two numbers. I've been trying to convert the euclidean algorithm into c++ and place it in a while loop but I feel like GCD is beyond me. I've got 3 pages of a notebook filled up with different ways of looking at the euclidean algorithm and I just can't comprehend what's going on. I can't understand how a mod operator would allow you to find a Greatest Common Divisor. Honestly, I'm just wanting someone to make this program for me but in a dumbed down way that I can understand.

Here's how it's supposed to work: User enters a pair of numbers separated by a space, then the program outputs the GCD. I'd prefer a while loop. Any takers?

[LB]

% gives you the remainder of division. A simple approach would be to loop through all numbers between 2 and the lowest of your two numbers and keep track of the largest number that has no remainder of division for both numbers.

[integralfx]

Let's say you want to find the greatest common divisor for 8 and 12.

for (int i = 12; i >= 2; i--)

Start looping at the larger number (12), checking the remainder when the numbers are divided by i (8 % i) and (12 % i)
If the modulo of both the numbers are 0, we have found the greatest common divisor.

i = 12
8 % 12 = 8
12 % 12 = 0

i = 11
8 % 11 = 8
12 % 11 = 1

i = 10
8 % 10 = 8
12 % 10 = 2

...

i = 4
8 % 4 = 0
12 % 10 = 0

Both of the remainders are 0, so we found the greatest common divisor (4).

And if you can't find the greatest common divisor, by default it's 1.

[Wordz91]

I finally got the program working!
But how do I keep it running so that the user can keep typing in a new set of numbers after getting an output? I want it to revert back to where the user types in an input. And I want the program to be able to stop if they input 111.

[JLBorges]

https://en.wikipedia.org/wiki/Euclidean_algorithm#Implementations

int gcd( int a, int b ) // recursive version
{
    if( b == 0 ) return a<0 ? -a : a ;
    
    else return gcd( b, a%b ) ;
}

[LB]

int number_to_test;
while((std::cout << "Enter a number to test, or 111 to exit: ")
   && (std::cin >> number_to_test)
   && (number_to_test != 111)
)
{
    //your code here
}

[Wordz91]

Do you know how I can differentiate between 00 and 0 when the user enters this number? I want 00 to terminate the program, but entering a set of numbers like 0 7 to still work. So far, 0 7 terminates the program just like 00 does.

[LB]

Take input as a string and check for "00" before converting to a number.

Possibly helpful:
http://www.LB-Stuff.com/user-input