6.31

/* 6.31 Greatest Common Divisor
Deitel& Deitel C++ How to Program, 10th ed (Indian subcontinent adaptation)
Visual Studio Community 2019 */

#include <iostream>
using namespace std;

int greatest(int integer1, int integer2 ) {
    int remainder{ 0 };
    if (integer1 == integer2) return integer1; // special case where the ints are equal
    for (int testNum = integer1 / 2; testNum > 0; testNum--) {
        if (integer1 % testNum == 0) { // found a candidate
            if (integer2 % testNum == 0) return testNum;
        }
    }
    return 1;
}

int main() {
    int int1{ 0 }, int2{ 0 }, gcd;
    while (true) {
        cout << "Enter two integers (or enter -1 to quit)" << endl << endl;
        cout << "First integer: ";
        cin >> int1;
        if (int1 == -1) break;
        cout << endl << "Second integer: ";
        cin >> int2;
        if (int2 == -1) break;
        gcd = greatest(int1, int2);
        cout << endl << "Greatest common divisor: " << gcd << endl << endl;
    }
    return 0;
}