MODULE bt;

	CONST MAXSIZE = 128;
	
	VAR
			s : ARRAY MAXSIZE OF INTEGER;
			i : INTEGER;

	PROCEDURE btParent*( n : INTEGER ): INTEGER;
	
		BEGIN
			IF n > MAXSIZE THEN
				RETURN ( -2 );
			ELSE
				IF n = 1 THEN
					RETURN 1;
				ELSE
					RETURN ( n DIV 2 );
				END;
			END;
		
		END btParent;

	PROCEDURE btLeftChild* ( n :INTEGER ): INTEGER;
	
		BEGIN
			IF  n  > MAXSIZE THEN 
				RETURN (-2);
			ELSIF 2 * n > MAXSIZE THEN
				RETURN ( -1 );
			ELSE
				RETURN (2 * n);
			END;
		
		END btLeftChild;

	PROCEDURE btRightChild* ( n :INTEGER ): INTEGER;
	
		BEGIN
			IF  n > MAXSIZE THEN 
				RETURN (-2);
			ELSIF (2 * n) + 1 > MAXSIZE THEN
				RETURN ( -1 );
			ELSE
				RETURN ((2 * n) + 1);
			END;
		
		END btRightChild;
		
	PROCEDURE btGetVal* ( n : INTEGER ) :INTEGER;
	
		BEGIN
			IF n > MAXSIZE THEN
				RETURN ( -2 );
			ELSE
				RETURN s[n - 1];
			END;
		END btGetVal;

	PROCEDURE btSetVal* ( n, i: INTEGER ) : INTEGER;
	
		BEGIN
			IF n > MAXSIZE THEN
				RETURN ( -2 );
			ELSE
				s[n - 1] := i;
				RETURN 0;
			END;
		END btSetVal;
				

	BEGIN
		i := 0;
		REPEAT  s[i] := 0; i := i + 1; UNTIL i >= MAXSIZE;
	END bt.
	
	
System.Free bt ~

bt.test