question about a type in pascal

Hi,
it's a simple question i know but it's the base of all my program
i have to take a random number out of 2, 3, 5 and 7
how do i proceed ???

temp:=Random(2, 3, 5, 7);
doesn't seem to work

a type ??
TYPE
 Primes=(2, 3, 5, 7);
a get a message error asking for a type or something like that
"Identifier Expected"

tell me please
thanks a lot
 
Elvis1Asked:
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mlmccCommented:
I would generate a random number between 1-4 and use that as an index into an array with those values

type
     P_array =  array[1..4] of integer;

var
     Rand_Index  : integer;
     Primes : P_array;


begin
     Primes [1] := 2;
     Primes [2] := 3;
     Primes [3] := 5;
     Primes [4] := 7;

     randomize;
     Rand_index := 4*random +1;

     writeln (Primes[Rand_Index]);

end.

mlmcc
   
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Wim ten BrinkSelf-employed developerCommented:
Good answer, mlmcc. However, I would suggest some minor alterations:

1) use an "P_array = array[0..3] of Integer;".
2) use "Rand_index := Random(4);"

And perhaps the Pascal version used can define arrays of constants like this:

const
  Primes : P_array = (2, 3, 5, 7);

Good answer, though. You deserve all credit in my opinion. ;-)
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mlmccCommented:
Glad I could help


Alex:
I grew up with arrays being 1-based so I tend to keep them like that.

Does Random(4) give a number from 0 to 3.999999?

I don't think Pascal allows constant arrays but it might.  Been too long since I used them.

mlmcc
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Wim ten BrinkSelf-employed developerCommented:
mlmcc:
I know, in Basic arrays used to be 1-based. However, when I learned Pascal a couple of decades ago I was told that arrays have user-definable upper and lower bounds. I do prefer to use 0-based arrays, though. Don't know why but it's just a preference...

Random(4) returns either 0, 1, 2 or 3. Nothing more, nothing less. At least in Turbo Pascal and Delphi.

I know Delphi allows constant arrays. I even use them quite often. I'm not sure but I think Turbo Pascal allows constant arrays too. But it's too long ago that I wrote my last TP application.
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mlmccCommented:
Alex: In VB arrays are 0-based.  I learned in FORTRAN IV.  I used to teach Pascal and we generally used arrays as 1 based.  I know you can set the index to be anything (one of the features of Pascal I really like).

mlmcc

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