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From: "Mark Lundquist" <mlundquist2@attbi.com>
Newsgroups: comp.lang.ada
References: <3C163FBE.9CB75916@rz.uni-karlsruhe.de>
Subject: Re: Unconstrained arrays
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"Michael Unverzagt" <uhcm@rz.uni-karlsruhe.de> wrote in message
news:3C163FBE.9CB75916@rz.uni-karlsruhe.de...
> Hi!
>
> We have to write a programm that uses an unconstrained array of
> ustrings, where the size of the array should be determined by user
> input...
>
> How does this work? Someone told me, I have to use subtypes but...
> Does anyone know a simple example where I can learn how I can define the
> size of an array at runtime by user input?

Hi Mike,

The first thing to understand is that in Ada, the bounds of an array need
not be static (they are constant, but need not be static).  So they can be
determined by a variable, a non-static constant, or some other non-static
expression like a function call, and the array will likely be allocated from
the stack, not the heap, and in any case you don't need any pointers or
explicit heap allocation.  So, two ways to do it:

Way 1:

procedure Main_Program is
    .
    .
    Array_Size : Natural;
    .
    .
begin
    .
    . -- Get input from the user
    . -- into the variable Array_Size
    .
    declare
        My_Array : array (1 .. Array_Size) of Foo;
    begin
        .
        .    -- do your thing...


Way 2:

procedure Main_Program is
    .
    .
    function Array_Size return Natural is
        Size_From_User : Natural;
    begin
        . - get input from user
        .
        .
        return Size_From_User ;
    end Array_Size;

    My_Array (1 .. Array_Size) of Foo;

begin
    .
    .
    .


Have fun,
-- Mark