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From: Jacob Sparre Andersen <sparre@nbi.dk>
Newsgroups: comp.lang.ada
Subject: Re: Question from newbie
Date: 16 Feb 2004 12:20:42 +0100
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Cecilia Chew worte:

> 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

>        Left : Character;
>        Right : Character;

These two identifiers are already used for the parameters passed to
the procedure.  And I don't think you want those variables anyway.

>        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);

I think you might want to insert a call to Ada.Text_IO.Skip_Line here.
Just to eat the newline entered after the number.

>     New_Line;
>     if Num not in Index then
>        Put ("Please enter 1 to 10 characters only!");
>     else
>        Put ("Please enter" & Integer'Image(Num) & " characters : ");

>        for num in Index loop

It is a little bit dangerous to use the name of an existing variable
for the counter in a for loop.  I think you actually wanted to write:

         for Character_Number in Index'First .. Num loop;

>           Get (Input (Num));

And this line was probably intended (as it did) to use the counter
from the for loop:

            Get (Input (Character_Number));

>           if Input'Length = num then

Input has a fixed length (10), so this will only be true, when you
have entered exactly 10 characters.

> 
>              for I in 1 .. num loop
> 	       Ascending_char (Input(i), Input(i+1));
>              end loop;
> 	
> 	    while not End_Of_Line loop
> 	       Put (Input(Num));
> 	    end loop;
> 	
> 	else
> 	    exit;
> 	end if;
> 	
>        end loop;
> end if;
> end Sort;
> =============================================================================
> Question:
> 1.  As the procedure ascending compiles as a independent unit with the
>      other file name, it could sort the two characters correctly.
>      However, as I put it together with sort.adb program. Specification
>      part that declared the procedure ascending conflict with the
>      variable left and right. Where is the mistake?

The mistake is that you have parameters and variables of the same
type.

> 2.  Before plug in the procedure ascending, the program successfully
>      being compiled. But the program can't allocate the specified space
>      as x characters in outputting the result. For an example, user
>      specified 2 characters, but the program still allow user to input
>      less than or excess 2 characters..Where is the mistakes?

The mistake is that you fix the length of the string to 10 characters
at compile time.

> 3.  From my coding, what should I pay more attention to?

You should be careful about using name overloading (until you are a
bit more sure about what you are doing).

You should look a bit more at how arrays are allocated and used in Ada
(your use of 'Length seems like you haven't understood it properly).

Greetings,

Jacob
-- 
"I've got _plenty_ of common sense!"
"I just choose to ignore it."