casting types

casting types

[Stribor40]

I have problem understanding this explicit conversion of types....

 var1: FLOAT;
 
 tmp := Float(x) / 20.0 + Float(y)/ 30.0 + Float(z)/40.0;
 return var1 - truncated type of var1

Example if var1 = 123.456 then
  return  123.456 - 123 

which is 0.123

How would I cast var1 to become 123 but still be able to subtract it from var1 and keep float type?

Re: casting types

[Jeffrey Carter]

On 09/30/2014 06:49 PM, Stribor40 wrote:
> 
> How would I cast var1 to become 123 but still be able to subtract it from var1 and keep float type?

You can't, since there is no casting in Ada. However, you might find the
'Truncation attribute function useful.

http://www.adaic.org/resources/add_content/standards/12rm/html/RM-A-5-3.html

-- 
Jeff Carter
"Nobody expects the Spanish Inquisition!"
Monty Python's Flying Circus
22

Re: casting types

[Stribor40]

On Tuesday, 30 September 2014 22:06:58 UTC-4, Jeffrey Carter  wrote:
> On 09/30/2014 06:49 PM, Stribor40 wrote:
> 
> > 
> 
> > How would I cast var1 to become 123 but still be able to subtract it from var1 and keep float type?
> 
> 
> 
> You can't, since there is no casting in Ada. However, you might find the
> 
> 'Truncation attribute function useful.
> 
> 
> 
> http://www.adaic.org/resources/add_content/standards/12rm/html/RM-A-5-3.html
> 
> 
> 
> -- 
> 
> Jeff Carter
> 
> "Nobody expects the Spanish Inquisition!"
> 
> Monty Python's Flying Circus
> 
> 22

Would you mind showing an example please...

Re: casting types

[Stribor40]

ok so i tried truncation attribute and that works just great. Now I want to output this float point to the screen and this is the way i did it....myFunction is myFunction that returns float....

Put(Item=>myFunction,Exp=>0,Aft=>5);

which gives me for example something like this... 0.42997 where without using this function i would get for example  3.23684E-01.....

Is there any other way to do this? 

Re: casting types

[Dennis Lee Bieber]

On Tue, 30 Sep 2014 19:56:59 -0700 (PDT), Stribor40 <ikamzic@gmail.com>
declaimed the following:

>ok so i tried truncation attribute and that works just great. Now I want to output this float point to the screen and this is the way i did it....myFunction is myFunction that returns float....
>
>Put(Item=>myFunction,Exp=>0,Aft=>5);
>
>which gives me for example something like this... 0.42997 where without using this function i would get for example  3.23684E-01.....
>

	Unless your function is really corrupting things, I expect the second
to be 4.2997E-01

	Floating point values (in any programming language) do not behave as
"real numbers"... One) they are stored as binary floats, not decimal, so
don't expect exact conversions in/out. Two) they are stored as an exponent,
and a mantissa of the significant binary value -- no 0.00001, rather 1.0E-5
[if I counted correctly].

	So, yes, you do have to control the formatting for display purposes.


	Your original post isn't too clear either...

>I have problem understanding this explicit conversion of types....
>
> var1: FLOAT;
> 
> tmp := Float(x) / 20.0 + Float(y)/ 30.0 + Float(z)/40.0;

	Do these serve any purpose? Neither tmp, x, y, z are declared or
initialized

> return var1 - truncated type of var1
>
>Example if var1 = 123.456 then
>  return  123.456 - 123 
>
>which is 0.123
>
	123.456 - 123 should leave 0.456

>How would I cast var1 to become 123 but still be able to subtract it from var1 and keep float type?
>Is there any other way to do this? 

-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

Re: casting types

[Stribor40]

I want to be able to represent numbers like 0.1234,-1,2345 and so on so thats why I chose float. Is there any other way i can represent numbers like that? Is there any other data type?

Re: casting types

[G.B.]

On 01.10.14 15:55, Stribor40 wrote:
> I want to be able to represent numbers like 0.1234,-1,2345 and so on so thats why I chose float. Is there any other way i can represent numbers like that? Is there any other data type?
>

Are these rational numbers 0.1234, whole number -1,
and whole number 2345, respectively?

The first falls under either floating point types
or decimal fixed point types, the second is of some
integer type, as is the last one.  You should be
able to learn how you can define just the types
that you need, by using really any text on Ada, no matter
how old.

Frequently, there is no need to use any predefined types.
These may neither reflect your problem well, nor let you
see how to use types. If you follow any tutorial text that
you like, it will let you see what numeric types these are:

    type Part_No is range 1_000 .. 9_999;

    type Bits_16 is mod 2**16;

    type Temperature is delta 0.1 digits 4;

    type Flt is digits 6 range 0.0 .. 42_000_000.0;

Re: casting types

[Stribor40]

i would like to represent all numbers in interval [0, 1]

Re: casting types

[Dirk Heinrichs]

Stribor40 wrote:

> i would like to represent all numbers in interval [0, 1]

Well, according to what I've learned in mathematics, you can't. Neither in 
real life, nor in any programming language. You need to define some 
constraint, like number of digits after the decimal point.

Bye...

	Dirk
-- 
Dirk Heinrichs <dirk.heinrichs@altum.de>
Tel: +49 (0)2471 209385 | Mobil: +49 (0)176 34473913
GPG Public Key CB614542 | Jabber: dirk.heinrichs@altum.de
Tox: heini@toxme.se
Sichere Internetkommunikation: http://www.retroshare.org
Privacy Handbuch: https://www.privacy-handbuch.de

Re: casting types

[Dennis Lee Bieber]

On Wed, 01 Oct 2014 19:38:22 +0200, Dirk Heinrichs
<dirk.heinrichs@altum.de> declaimed the following:

{responding to Stribor40}

>Stribor40 wrote:
>
>> i would like to represent all numbers in interval [0, 1]
>
>Well, according to what I've learned in mathematics, you can't. Neither in 
>real life, nor in any programming language. You need to define some 
>constraint, like number of digits after the decimal point.
>
	And on most machines these days -- you can expect the hardware to
support single precision (32-bit) with ~7 significant digits, double
precision (64-bit) with ~15 significant digits... And only within the
floating point processor, maybe IEEE 80-bit (downconverted when the final
result is returned to the user).

	Note that "significant digits" does not take into account the decimal
point...

	12300000.0, 1.23, 0.00000123

all have 3 significant digits if they are /floating point/ values (they are
all 1.23E<some exponent>)


	Fixed point types are closer to integers with an implied decimal point.
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

Re: casting types

[Jeffrey Carter]

On 10/01/2014 06:55 AM, Stribor40 wrote:
> Is there any other data type?

In Ada, the question shouldn't be "Is there any other data type?" (or "Which
language-defined type should I use?"), but rather "What type should I declare
for these values?" Ada is unique among mainstream languages in allowing the
developer to declare numeric types that reflect the problem domain, and
McCormick found this to be part of the most important reason ("Modeling of
scalar objects") why his students succeeded with Ada.

http://www.crosstalkonline.org/storage/issue-archives/2000/200008/200008-McCormick.pdf

-- 
Jeff Carter
"I'm a kike, a yid, a heebie, a hook nose! I'm Kosher,
Mum! I'm a Red Sea pedestrian, and proud of it!"
Monty Python's Life of Brian
77

Re: casting types

[Brian Drummond]

On Wed, 01 Oct 2014 06:55:31 -0700, Stribor40 wrote:

> I want to be able to represent numbers like 0.1234,-1,2345 and so on so
> thats why I chose float. Is there any other way i can represent numbers
> like that? Is there any other data type?

Yes, there is also fixed point, though I have a feeling this is a trivial 
answer because you haven't quite got to the real question.

- Brian

Re: casting types

[Brian Drummond]

On Tue, 30 Sep 2014 19:56:59 -0700, Stribor40 wrote:

> ok so i tried truncation attribute and that works just great. Now I want
> to output this float point to the screen and this is the way i did
> it....myFunction is myFunction that returns float....
> 
> Put(Item=>myFunction,Exp=>0,Aft=>5);
> 
> which gives me for example something like this... 0.42997 where without
> using this function i would get for example  3.23684E-01.....
> 
> Is there any other way to do this?

At this point it's not clear what "do this" means or why the second 
example is a scientific notation representation of a completely different 
number.

Put together the smallest complete compilable example of the problem you 
see, and it will help the discussion along wonderfully.

- Brian

Re: casting types

[Stribor40]

Ok basically what I want to do now is following...

I am trying to print out my float to the screen by doing following..


Put(myFunction);

Where myFunction generates number 9.24543E-01 which is output to the screen..
I can also output it like this 

Put(Item=>Float 'Truncation(120.00*myFunction),Exp=>0,Aft=>5);

to output  81.00000 to the screen.


Now I would like to save this  81.00000 as an integer to some variable. Can you please show me how to do this please

Re: casting types

[Björn Lundin]

On 2014-10-03 05:35, Stribor40 wrote:
> Ok basically what I want to do now is following...
> 
> I am trying to print out my float to the screen by doing following..
> 
> 
> Put(myFunction);
> 
> Where myFunction generates number 9.24543E-01 which is output to the screen..
> I can also output it like this 
> 
> Put(Item=>Float 'Truncation(120.00*myFunction),Exp=>0,Aft=>5);
> 
> to output  81.00000 to the screen.
> 
> 
> Now I would like to save this  81.00000 as an integer to some variable. Can you please show me how to do this please
> 
> 
> 
> 

declare
  An_Integer : Integer := Integer(Float'Truncation(120.00*myFunction));
begin
  Text_io.Put_Line(Integer'Image(An_Integer));
end;


--
Björn

Re: casting types

[Jacob Sparre Andersen]

Stribor40 wrote:

> Now I would like to save this 81.00000 as an integer to some
> variable. Can you please show me how to do this please

You can't do that without having declared (or chosen) an appropriate
integer type, and declared a variable of that type.

Once that is done, you write:

   Variable := Type (81.00000);

Greetings,

Jacob
-- 
"constructive ambiguity"

Re: casting types

[brbarkstrom]

On Friday, October 3, 2014 4:29:34 AM UTC-4, Jacob Sparre Andersen wrote:
> Stribor40 wrote:
> 
> 
> 
> > Now I would like to save this 81.00000 as an integer to some
> 
> > variable. Can you please show me how to do this please
> 
> 
> 
> You can't do that without having declared (or chosen) an appropriate
> 
> integer type, and declared a variable of that type.
> 
> 
> 
> Once that is done, you write:
> 
> 
> 
>    Variable := Type (81.00000);
> 
> 
> 
> Greetings,
> 
> 
> 
> Jacob
> 
> -- 
> 
> "constructive ambiguity"

First, to be safe in doing any floating point arithmetic, you should
use the Ada type long_float.  You can rename this to double or real
if you want.  Create a package that that creates a new Ada.Numerics
(or some such - I need to check the definitions I usually use on my Windows
XP machine that doesn't connect to the Web)

Next, the equivalent to type casting is that you can then create a function
like

With Common_Defs; use Common_Defs;

function Multiply(x : in     float;
                  y : in     float) return real;

function Multiply(x : in     float;
                  y : in     float) return real
is
   Result : real;
begin
   Result := real(x*y);
   return (Result);
end Multiply;

You will reduce both truncation and round-off errors by doing all
floating point computations with Ada long_float variables and 
operations.  If you do, just replace the "float" types in the
snippet with "real" and carry on.  If you need an introduction,
consult Acton, 1970: "Numerical Methods That Work", Haroer & Row.
It's the only book I know on numerical methods that has a sense of
humor - as well as a whole interlude on "What Not To Compute".

Bruce B.

Re: casting types

[Jeffrey Carter]

On 10/06/2014 04:36 PM, brbarkstrom@gmail.com wrote:
> 
> First, to be safe in doing any floating point arithmetic, you should
> use the Ada type long_float.

No, you shouldn't. First, Long_Float is optional; there is no guarantee that a
compiler implements it, so if you want your code to be portable you'll avoid it.
Even if it is defined, it need not be any different from Float. Second, given
that McCormick identified modeling scalars (using user-defined numeric and
enumeration types) as the main Ada feature that allowed his students to be
successful, advice to always use a predefined type should rightly be regarded
with suspicion.

If you have an application that needs the maximum precision the compiler can
give you, you should define a floating-point type using System.Max_Digits.

>    return (Result);

There is no need for parentheses here.

-- 
Jeff Carter
"I was hobbling along, minding my own business, all of a
sudden, up he comes, cures me! One minute I'm a leper with
a trade, next minute my livelihood's gone! Not so much as a
'by your leave!' You're cured, mate. Bloody do-gooder!"
Monty Python's Life of Brian
76

Re: casting types

[brbarkstrom]

On Monday, October 6, 2014 8:03:44 PM UTC-4, Jeffrey Carter wrote:
> On 10/06/2014 04:36 PM, brbarkstrom@gmail.com wrote:
> 
> > 
> 
> > First, to be safe in doing any floating point arithmetic, you should
> 
> > use the Ada type long_float.
> 
> 
> 
> No, you shouldn't. First, Long_Float is optional; there is no guarantee that a
> 
> compiler implements it, so if you want your code to be portable you'll avoid it.
> 
> Even if it is defined, it need not be any different from Float. Second, given
> 
> that McCormick identified modeling scalars (using user-defined numeric and
> 
> enumeration types) as the main Ada feature that allowed his students to be
> 
> successful, advice to always use a predefined type should rightly be regarded
> 
> with suspicion.
> 
> 
> 
> If you have an application that needs the maximum precision the compiler can
> 
> give you, you should define a floating-point type using System.Max_Digits.
> 
> 
> 
> >    return (Result);
> 
> 
> 
> There is no need for parentheses here.
> 
> 
> 
> -- 
> 
> Jeff Carter
> 
> "I was hobbling along, minding my own business, all of a
> 
> sudden, up he comes, cures me! One minute I'm a leper with
> 
> a trade, next minute my livelihood's gone! Not so much as a
> 
> 'by your leave!' You're cured, mate. Bloody do-gooder!"
> 
> Monty Python's Life of Brian
> 
> 76
Thanks for the correction.