Hi,
I',m not sure but I think I'm allowed to post questions here showing my own work. I have the following question (not homework or anything assessed - Im revising for my final exam and this is a past paper question that i dont have model answers to).

I'd appreciate any help. I think It's relatively simple but I am unfamiliar with pascal and unsure of my own answers.

Question
a) Each of these definitions of a type is expressed in a PASCAL-like notation. For each right hand side:


1) Express it in terms of set-operations.2) Indicate one representative member of the set that it defines.3) Give its size.



TYPE

Colour = (yellow, red, blue, green);

Charr = ['a'..'z'];

Integerr = [1..99];

String = ARRAY[0..10] OF Charr;

Info = RECORD

I : Integerr;

S : String;

C : Colour;

END (*RECORD*);

vrec = RECORD

CASE card : CARDINAL OF

0 : I : Integerr;

|1 : C : Colour;

|2 : CC : Charr;

END (*CASE*);

END (*RECORD*);

hue = SET OF Colour;



My Answers

1) Express it in terms of set-operations.

(yellow, red, blue, green)
={ (x1, x2, x3, x4)| x1 Î yellow, x2 Î red, x3 Î blue, x4 Î green}} ???

['a'..'z']
={ a|aÎ {a,b,c, …, z}}

[1..99]
={ a|aÎ {1, 2, 3, 4, …, 99} }

ARRAY[0..10] OF Charr;={ [a0, a2, …, a10]| aiÎ Charr}


Info = RECORD
I : Integerr;
S : String;
C : Colour;
END (*RECORD*);={ I, S, C | IÎ Integerr, SÎString, CÎColour }



vrec = RECORD
CASE card : CARDINAL OF
0 : I : Integerr;|1 : C : Colour;|2 : CC : Charr;
END (*CASE*);
END (*RECORD*);=?????? ???????

?=Check cardinality of ‘card’:

If 0 then assign I as integer

If 1 then assign C as Colour

If 2 then assign CC as Charr




hue = SET OF Colour;
={ x | x Î (yellow, red, blue, green)



2) Indicate one representative member of the set that it defines.


(yellow, red, blue, green)
=(yellow, red, blue, green) ???

['a'..'z']=‘a’

[1..99]=1

ARRAY[0..10] OF Charr;
=[a, b, c, d, e, f, g, h, I, j]


Info = RECORD
I : Integerr;
S : String;
C : Colour;
END (*RECORD*);
={I=1, S=[a, b, c, d, e, f, g, h, I, j], C=(yellow, red, blue, green)}


vrec = RECORD
CASE card : CARDINAL OF
0 : I : Integerr;|1 : C : Colour;|2 : CC : Charr;
END (*CASE*);
END (*RECORD*);
=?????????????

hue = SET OF Colour;
={ (x1, x2, x3, x4)| xi Î Colour}



OK. Phew!!

vrec = Im stuk with this. Although I have worked out that:
------------------------------
vrec = RECORD
CASE card : CARDINAL OF
0 : I : Integerr;
|1 : C : Colour;
|2 : CC : Charr;
END (*CASE*);
END (*RECORD*);
------------------------------

Is probably equal to:

------------------------------|
vrec = RECORD
CASE card : CARDINAL OF
0 : I : Integerr;|1 : C : Colour;|2 : CC : Charr;
END (*CASE*);
END (*RECORD*);
------------------------------

The '|' sign is the logical 'or'. I'm also guessing that first the CARDINALITY of 'card' is first taken and cardinality is the number of members of the set called 'card'. Therefore when the cardinality is worked out, if it's 0 then the variable I is assigned the datatype Integerr, when its 1 the variable C is assigned the datatype Colour, and when its 2 the variable CC is assigned the datatype Charr.

As you can see i can't really answer parts 2 and 3 if im not sure of part 1. :cry:

I'd appreciate any help you can provide.

Thank you.