#! This program computes the GCD of two positive integers
#! using the Euclid method.  Given a and b, a >= b, the
#! Euclid method goes as follows:  (1) dividing a by b yields
#! a reminder c; (2) if c is zero, b is the GCD; (3) if c is
#! no zero, b becomes a and c becomes c and go back to
#! Step (1).  This process will continue until c is zero.

Using Pseudo code:

Define a,b,c as Integers
Input a ,b

IF (a < b) THEN          #! since a >= b must be true, they
      c = a              #! are swapped if a < b
      a = b
      b = c
   END IF

#!using Euclid's method we need to loop through the following
   DO
      c = MOD(a, b)      #!    compute c, the reminder
      IF (c == 0) EXIT   #!    if c is zero, we are done.  GCD = b
      a = b              #!    otherwise, b becomes a
      b = c              #!    and c becomes b
   END DO                #!    go back

   Print('The GCD is ', b)