Greatest Common Divisor Loop [duplicate]

Question

I'm doing some self-taught Java, but can't seem to figure out the issue in this loop:

The question was to find the greatest common divisor of two integers n1 and n2 where d is the lesser value. The method is to decrement d until a GCD or it reaches 1...here's where I'm at so far:

    Scanner input = new Scanner(System.in);
    System.out.println("Please enter two integers: ");
    int n1 = input.nextInt();
    int n2 = input.nextInt();

    int d = 0;
    int temp = 0;
    //finds the lowest value
    if(n1 < n2) {
        temp = n1;
        n1 = n2;
        n2 = temp;
    }

    for(d = n1;(n1 % d !=0 && n2 % d != 0);d--)  {

    }

    System.out.println("The GCD of " + n1 + " and " + n2 + " is " + d);

Any pointers?

Answer 1

The logic in here is wrong:

(n1 % d !=0 && n2 % d != 0)

change to:

(n1 % d !=0 || n2 % d != 0)

Or the code will stop once is saw a divisor of n1 or n2, instead of their GCD, since the loop termination condition should be the negation of what you want to do.

Answer 2

Iterative

public static long gcd(long a, long b){
   long factor= Math.max(a, b);
   for(long loop= factor;loop > 1;loop--){
      if(a % loop == 0 && b % loop == 0){
         return loop;
      }
   }
   return 1;
}

Iterative Euclid's Algorithm

public static int gcd(int a, int b) //valid for positive integers.
{
    while(b > 0)
    {
        int c = a % b;
        a = b;
        b = c;
    }
    return a;
}

Optimized Iterative

static int gcd(int a,int b)
    {
        int min=a>b?b:a,max=a+b-min, div=min;
        for(int i=1;i<min;div=min/++i)
            if(max%div==0)
                return div;
        return 1;
    }

Recursive

public static long gcd(long a, long b){
   if(a == 0) return b;
   if(b == 0) return a;
   if(a > b) return gcd(b, a % b);
   return gcd(a, b % a);
}

Built-in

import java.math.BigInteger;

public static long gcd(long a, long b){
   return BigInteger.valueOf(a).gcd(BigInteger.valueOf(b)).longValue();
}

via - http://rosettacode.org/wiki/Greatest_common_divisor