// This program should print the number 20.
program Twenty:
  int a;
  int b;
  a := 2;
  b := 1;
  if not (a < 0) then
    int b;
    b := - 2;     //     (the inner b, the outer one is still 1)
    a := a * b    // a = -4
  else
    int c;
    c := a - b;
    a := a * (c - b)
  fi;
  print a * (a - b)    // -4 * (-4 - 1)  =  -4 * (-5)  =  20
end
// This program should print the number 20.
program Twenty:
  int a;
  int b;
  a := 2;
  b := 1;
  while a >= 0 do
    int b;
    b := - 2;     // (the inner b, the outer one is still 1)
    a := a * b    // a = -4
  od;
  print a * (a - b)    // -4 * (-4 - 1)  =  -4 * (-5)  =  20
end
 // This program should print the number 20.
program Twenty2:
  int a;
  int b;
  a : = 2;
  b := 1;
  if not (a < 0) then
    int b;
    b := - 2;     //     (the inner b, the outer one is still 1)
    a := a * b    // a = -4
  else
    int c;
    c := a - b;
    a := a * (c - b)
  fi;
  print a * (a - b)    // -4 * (-4 - 1)  =  -4 * (-5)  =  20
end
// Euclid's algorithm for the greatest common divisor.
program GCD:
   int a;  int b;
   a := 15;
   b := 20;
   print a;  print b;
   while a != b do
      if a < b then b := b - a
      else a := a - b
      fi
   od;
   print a
end
program Hiding :
   int a;
   int b;
   a := 2;
   b := 5;
   while not (a != b) do
     int b;
     b := 2 * a;
     print b;
     a := a + 1
   od;
   print b
end
program condtional:
  if 3 < 3 then
    print false
  fi
end
program condtional2 :
  if 3<3 then print false fi
end
program lexicallyOk :
   intt a;
   int b;
   a :== 2;
   b := 5;
   while (a != b) do not print else do
     int b;
     b := 2 *** a;
     print b;
     a := a + 1
   od;
   print b
end
program lexically-Ok-2
   program Print:
  print(77)
end
program bad_expression:
   int a;
   int b;
   if4 a < b then5
     2int b;
     b := 2 * a
   5else
     bool b;
     b := 2 * a
   fii
end