Greatest common divisor

Greatest common divisor
You are encouraged to solve this task according to the task description, using any language you may know.

This task requires the finding of the greatest common divisor of two integers.

ALGOL 68

PROC gcd = (INT a, b) INT: (
  IF a = 0 THEN
    b
  ELIF b = 0 THEN
    a
  ELIF a > b  THEN
    gcd(b, a MOD b)
  ELSE
    gcd(a, b MOD a)
  FI     
);

main : (
  INT a = 33, b = 77;
  printf(($x"The gcd of"g" and "g" is "gl$,a,b,gcd(a,b)));
  INT c = 49865, d = 69811;
  printf(($x"The gcd of"g" and "g" is "gl$,c,d,gcd(c,d)))
)

The output is:

The gcd of        +33 and         +77 is         +11
The gcd of     +49865 and      +69811 is       +9973

Forth

: gcd ( a b -- n )
  begin dup while tuck mod repeat drop ;

Java

Iterative

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

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);
}