Re: Numerical calculations: Why not use fixed point types for everything?

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 13-02-04 08:23 , Ada novice wrote:
> On Sunday, February 3, 2013 5:05:22 AM UTC+1, Shark8 wrote:
>>
>>
>>     Type P is delta 0.1 digits 3 range 0.0..10.0;
>>
>>     
>>
>>     declare
>>
>> 	Index : P := P'First;
>>
>>     begin
>>
>> 	loop
>>
>> 	    Ada.Text_IO.Put_Line( Index'Img );
>>
>> 	    Exit when Index = P'Last;
>>
>> 	    Index:= P'Succ(Index);
>>
>> 	End loop;
>>
>>     end;
>>
> 
> I was working an example based on the working code you gave:
> 
> with Ada.Text_IO;
> with Ada.Long_Float_Text_IO;
> 
> procedure Test is
> 
> type P is delta 0.1 digits 3 range 0.0..10.0;
> 
>         Index: P := P'First;
>         Number   : Long_Float := 100.0;
> 
> 
>    begin
>       loop
>          Ada.Text_IO.Put(Index'Img);Ada.Text_IO.Put("  ");
> 
>          Ada.Long_Float_Text_IO.Put (Item => Long_Float(Index)*Number, Fore => 3, Aft  => 3, Exp  => 0);Ada.Text_IO.Put("  ");
> 
>          --Number := Long_Float(Index)*Number;
>          Ada.Long_Float_Text_IO.Put (Item => Number, Fore => 3, Aft  => 3, Exp  => 0);
> 
>          Ada.Text_IO.New_Line;
> 
>          exit when Index = P'Last;
> 
>          Index := P'Succ(Index);
> 
> 
>       end loop;
> 
> end Test;
> 
> 
> On running I get:
> 
>  0.0    0.000  100.000
>  0.1   10.000  100.000
>  0.2   20.000  100.000
>  0.3   30.000  100.000
>  0.4   40.000  100.000
>  0.5   50.000  100.000
> ... and so on
> 
> which is expected.
> 
> Now, when I un-comment the line 
> 
> --Number := Long_Float(Index)*Number;
> 
> and run the code again, I get:
> 
>  0.0    0.000    0.000
>  0.1    0.000    0.000
>  0.2    0.000    0.000
>  0.3    0.000    0.000
>  0.4    0.000    0.000
>  0.5    0.000    0.000
> 
> ... and so on.
> 
> This is a weird behaviour.

No, it is expected.

> Why are the second and third columns all zeros now?

On the first iteration of the loop, Index = 0.0. Therefore the
uncommented statemement assigns the value Long_Float (0.0) * Number,
which is zero, to Number. In the next iteration the same statement
assigns Long_Float (0.1) * Number, which is again zero, to Number. So
Number stays at zero throughout the loop.

Perhaps you intended to assign a different variable? As in

   Number2 := Long_Float (Index) * Number;


-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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