// The basic I/O library available is built on three primitives,
// get(int *ch), peek(int *ch), and put(int ch).  Get and
// peek both read from stdin.  Peek leaves the character
// unread.  EOF returns -1.  Put writes to stdout.  Programs
// must be invoked on Unix as   "prog < infile > outfile".
// They are not meant for interactive I/O and buffering
// is undefined.

// Note that get and peek *must* have signed ints as
// parameters.  Put may be given a char etc because it
// will be type coerced automatically to the encompassing
// int type.

// On windows, character 13 is stripped on input, and
// added on output after character 10 is put.

procedure Mod (unsigned int M, N, unsigned int *result)
begin
  *result = M - ((M/N) * N)
end

procedure writeu(unsigned int num)
begin
  // write num with no leading spaces or zeroes.
  if (num > 10) writeu(num/10) endif
  Mod (num, 10, &num);
  put(num+'0');
end

procedure printstring(char *s)
begin
  int i;
  // print the string *literal* that is the parameter.
  i = 0
  while (s[i] != 0)
    put(s[i])
    i = i+1
  endwhile
end

procedure newline()
begin
  put(10)
end

procedure Gcd( unsigned int M, unsigned int N, unsigned int *result )
begin
  unsigned int Rem;
  while ( N > 0 )
    Mod(M, N, &Rem);
    M = N;
    N = Rem;
  endwhile
  *result = M;
end

program begin
  unsigned int val;

  Gcd( 45, 35, &val );
  printstring( "Gcd( 45, 35 ) = ");
  writeu(val); newline();
  Gcd( 1989, 1590, &val );
  printstring( "Gcd( 1989, 1590 ) = ");
  writeu(val); newline();
end