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From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: basic questions on using Ada arrays
Date: Wed, 06 Oct 2010 10:03:19 -0700
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Date: 2010-10-06T10:03:19-07:00
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On 10/06/2010 08:43 AM, Nasser M. Abbasi wrote:
>
> Also, is there a way to initialize an array using a formula or a
> function call? I know I can do
>
> x : array(1..nPoints) of float := (others => 0.0)
>
> But I wanted to make each entry in the array to have some value
> depending on the index value. I did not know how, so that is what the
> above small loop does, to initialize x array.

Certainly, but one must use a named array type, not anonymous types as you have 
done.

You can find examples of such functions in Ada.Strings.Fixed (ARM A.4.3). Type 
String is simply an array type. For example

X : String := 5 * 'x';

results is X having the subtype String (1 .. 5) and the value "xxxxx". This 
doesn't give a different value for each component, but it's easy enough to write 
one yourself:

function Digit_List (Length : in Natural) return String;
-- Returns a value of subtype String (1 .. Length) containing repeated
-- sequences of "1234567890". Each position contains the value of its
-- index modulo 10.

function Digit_List (Length : in Natural) return String is
    function Last_Digit (Value : in Positive) return Character;
    -- returns the Character representation of the last digit in the
    -- base 10 image of Value.

    function Last_Digit (Value : in Positive) return Character is
       Image : constant String := Integer'Image (Value);
    begin -- Last_Digit
       return Image (Image'Last);
    end Last_Digit;

    Result : String (1 .. Length);
begin -- Digit_List
    All_Digits : for I in Result'range loop
       Result (I) := Last_Digit (I);
    end loop All_Digits;

    return Result;
end Digit_List;

Column_Header : constant String := Digit_List (80);

Of course, all of this requires you to write loops. Loops may be "out of 
fashion", but Ada isn't about following fashion; if it were, it would look like 
C, not have all those inefficient run-time checks, and give far fewer 
compilation errors.

-- 
Jeff Carter
"Don't knock masturbation. It's sex with someone I love."
Annie Hall
45