Re: Question from newbie

[Adrian Hoe <AdrianHoe@nowhere.com>]

Jacob Sparre Andersen wrote:

> Cecilia Chew wrote:
> 
> 
>>with Ada.Text_Io, Ada.Integer_Text_Io;
>>use Ada.Text_Io, Ada.Integer_Text_io;
>>
>>procedure Sort is
>>    subtype Index is Integer range 1 .. 10;
>>    subtype Char is Character range 'a' .. 'z';
>>    type Str is array (Index) of Char;
>>    procedure Ascending (Left : in out Character; Right : in out
>>Character);
>>
>>    procedure Ascending (Left : in out Character; Right : in out
>>Character) is
>>
>>       Temp : Character;
>>    begin
>>       if Left > Right then
>>          Temp := Left;
>>          Left := Right;
>>          Right := Temp;
>>       end if;
>>    end Ascending;
>>
>>    Num : Index;
>>    Input : Str;
>>
>>begin
>>    Put ("Please enter the number of character : ");
>>    Get (Num);
>>    Ada.Text_Io.Skip_Line;
>>    New_Line;
>>    if Num not in Index then
> 
> 
> This check should not be necessary.  Since "Num" is of the subtype
> "Index", it _can_ only have values that are in "Index".  You should on
> the other hand get a "Constraint_Error", if you try to enter a number
> that is not in the range of "Index".
> 
> 
>>       Put ("Please enter 1 to 10 characters only!");
>>    else
>>       Put ("Please enter" & Integer'Image(Num) & " characters : ");
>>       for Character_number in Index'First .. Num loop
>>	 Get (Input(Character_number));
> 
> 
> [ here's line 36 - I think ]
> 
> Did you actually enter "Num" characters in the range 'a' .. 'z'?
> 
> A "Constraint_Error" indicates that something is out of range.  It
> can't be "Character_Number", since both "Index'First" and "Num" are
> valid values of the subtype "Index" (and "Character_Number" thus
> always will be a valid index for the array "Input").
> 
> The alternative is that the character you entered wasn't in the valid
> range for "Input (Character_Number)", i.e. in the range 'a' .. 'z'.

No. That is fine. Look into line 36 carefully and you shall find the 
mistake. :)
-- 
Adrian Hoe
m a i l b o x AT a d r i a n h o e . c o m