MODULE TwentyFour;

FROM	InOut			IMPORT WriteString, WriteLn, Write, ReadString, WriteInt;
FROM	RandomGenerator IMPORT Random;

TYPE	operator_t 		= (add, sub, mul, div);
		expr_t			= RECORD
							operand		: ARRAY[0..3] OF CARDINAL;
					  		operator 	: ARRAY[1..3] OF operator_t;
						  END;(*of RECORD*)
		numbers_t		= SET OF CHAR;

VAR		expr 	: expr_t;
		numbers	: numbers_t;
(*******************************************************************createExpr*)
(*analyse the input string                                                    *)
PROCEDURE createExpr(s: ARRAY OF CHAR);

VAR index, counter	: INTEGER;
	token 			: CHAR;
	temp_expr 		: expr_t;
	operand   		: CARDINAL;
	operator		: operator_t;
	
	(************************************nextToken*)
	(* returns the next CHAR that isn`t a space    *)
	PROCEDURE nextToken(): CHAR;
	BEGIN
		INC(index);
		WHILE (s[index] = ' ') DO
			INC(index);
		END;(*of WHILE*)
		RETURN(s[index]);
	END nextToken;
	(***********************************set_operand*)
	(* checks if the CHAR o inerhits a valid number*)
	(* and sets 'operand' to its value             *)	
	PROCEDURE set_operand(o: CHAR);
	BEGIN
		CASE o OF
			'0'..'9':	IF o IN numbers THEN
							operand := ORD(o)-48;
							numbers := numbers - numbers_t{o};
						ELSE
							WriteString("ERROR: '");
							Write(					o);
							WriteString(				"' isn`t a available number ");
							WriteLn;
							HALT;
						END;(*of IF*)|
			0  : WriteString("ERROR: error in input ");
					WriteLn;
					HALT;
			ELSE
				WriteString("ERROR: '");
				Write(					o);
				WriteString(				"' isn`t a number ");
				WriteLn;
				HALT;
		END;(*of CASE*)
	END set_operand;
	(**********************************set_operator*)
	(* checks if the CHAR o inerhits a valid       *)
	(* operator and sets 'operator' to its value   *)
	PROCEDURE set_operator(o: CHAR);
	BEGIN
		CASE o OF
			'+' : operator := add;|
			'-' : operator := sub;|
			'*' : operator := mul;|
			'/' : operator := div;|
			0  : WriteString("ERROR: error in input ");
					WriteLn;
					HALT;
		ELSE
			WriteString("ERROR: '");
				Write(					o);
				WriteString(				"' isn`t a operator ");
				WriteLn;
				HALT;
		END;(*of CASE*)
	END set_operator;
	(************************************************)
BEGIN
	index := -1;
	
	token := nextToken();
	set_operand(token);
	expr.operand[0] := operand;
	
	token := nextToken();
	set_operator(token);
	expr.operator[1] := operator;
	
	
	token := nextToken();
	set_operand(token);
	expr.operand[1] := operand;
	
	token := nextToken();
	set_operator(token);
	expr.operator[2] := operator;
	
	token := nextToken();
	set_operand(token);
	expr.operand[2] := operand;
	
	token := nextToken();
	set_operator(token);
	expr.operator[3] := operator;
	
	token := nextToken();
	set_operand(token);
	expr.operand[3] := operand;
END createExpr;

(*****************************************************************evaluateExpr*)
(* evaluate the expresion that was createt by 'createExpr'                    *)

PROCEDURE evaluateExpr(VAR num: REAL);

VAR	index	: INTEGER;
BEGIN
	WITH expr DO
		num := VAL(REAL,operand[0]);
		FOR index := 1 TO 3 DO
			CASE operator[index] OF
				add : num := num + VAL(REAL,operand[index]);|
				sub : num := num - VAL(REAL,operand[index]);|
				mul : num := num * VAL(REAL,operand[index]);|
				div : num := num / VAL(REAL,operand[index]);
			END;(*of CASE*)
		END;(*of FOR*)
	END;(*of WITH*)
END evaluateExpr;

(**************************************************************generateNumbers*)
(* generates the 4 random numbers ond write them                              *)
PROCEDURE generateNumbers;
VAR	index,ran : INTEGER;
BEGIN
	numbers := numbers_t{};
	ran := Random(0,9);
	FOR index := 1 TO 4 DO
		WHILE (CHR(ran+48) IN numbers )DO
			ran := Random(0,9);
		END;(*of While*)
		Write(CHR(ran+48));
		WriteLn;
		numbers := numbers + numbers_t{CHR(ran+48)}
	END;(*of FOR*)
END generateNumbers;
(****************************************************************Main Programm*)
VAR	str : ARRAY[0..255] OF CHAR;
	sum : REAL;
BEGIN
	WriteString("Welcome to the 24 game in MODULA-2");
	WriteLn;
	WriteString("Here are your numbers:");
	WriteLn;
	generateNumbers;
	WriteString("Enter your equation(This implementation dosn`t support brackets yet): ");
	WriteLn;
	ReadString(str);
	createExpr(str);
	evaluateExpr(sum);
	WriteLn;
	WriteString("Result:");
	WriteLn;
	WriteInt(TRUNC(sum),0);
	WriteLn;
	CASE (TRUNC(sum) - 24) OF
		0 : WriteString("Perfect!");|
		1 : WriteString("Almost perfect.");
		ELSE
			WriteString("You loose!");
	END;(*of CASE*)
	WriteLn;
END TwentyFour.