PASCAL: AN INTRODUCTION

ADDITIONAL OPERATIONS WITH USER DEFINED VARIABLE TYPES
Consider the following code,


	type Weekday = ( Monday, Tuesday, Wednesday, Thursday, Friday );
	var  Workday : Weekday;

The first symbol of the set has the value of 0, and each symbol which follows is one greater. Pascal provides three additional operations which are performed on user defined variables. The three operations are,

 ord( symbol )   returns the value of the symbol, thus ord(Tuesday)
                 will give a value of 1

 pred( symbol )  obtains the previous symbol, thus
                 pred(Wednesday) will give Tuesday

 succ( symbol )  obtains the next symbol, thus succ(Monday)
                 gives Tuesday

Enumerated values can be used to set the limits of a for statement, or as a constant in a case statement, eg,


	for Workday := Monday to Friday
	     .........

	case Workday of
	      Monday : writeln('Mondays always get me down.');
	      Friday : writeln('Get ready for partytime!')
	end;

Enumerated type values cannot be input from the keyboard or outputted to the screen, so the following statements are illegal,


	writeln( drink );
	readln( chair );

SELF TEST ON ENUMERATED DATA TYPES
Whats wrong with?


	type Day = (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday,
	            Sunday);
	var  Today : Day;

	for Today := Sunday to Monday do
	begin
	   writeln( Today );
	   Today := succ( Today )
	end;

Whats wrong with


	type COLOR = ( Red, Blue, Green, Yellow );
	var  Green, Red : COLOR;

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