Characters and Numerics

Characters and Numerics

[Duke Luke]

How can I change type character to type natural??
e.g: '3' -> 3;

(The character is always a number).

Please help me.

Re: Characters and Numerics

[Lutz Donnerhacke]

* Duke Luke wrote:
>How can I change type character to type natural??
>e.g: '3' -> 3;

S'Value denotes a function with the following specification:

  function S'Value(Arg : String) return S'Base;
  
This function returns a value given an image of the value as a String,
ignoring any leading or trailing spaces.
  
For the evaluation of a call on S'Value for an enumeration subtype S, if the
sequence of characters of the parameter (ignoring leading and trailing
spaces) has the syntax of an enumeration literal and if it corresponds to a
literal of the type of S (or corresponds to the result of S'Image for a
value of the type), the result is the corresponding enumeration value;
otherwise Constraint_Error is raised. For a numeric subtype S, the
evaluation of a call on S'Value with Arg of type String is equivalent to a
call on S'Wide_Value for a corresponding Arg of type Wide_String.

=> Natural'Value ((1 => '3'));

Re: Characters and Numerics

[M. A. Alves]

On 5 Dec 2001, Duke Luke wrote:
> How can I change type character to type natural??
> e.g: '3' -> 3;

Use attribute Value of the type Natural upon a String version of
the Character e.g.

  N := Natural'Value(C & "");

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Re: Characters and Numerics

[Matthew Heaney]

"M. A. Alves" <maa@liacc.up.pt> wrote in message
news:mailman.1007554622.31106.comp.lang.ada@ada.eu.org...
> On 5 Dec 2001, Duke Luke wrote:
> > How can I change type character to type natural??
> > e.g: '3' -> 3;
>
> Use attribute Value of the type Natural upon a String version of
> the Character e.g.
>
>   N := Natural'Value(C & "");

Or just

   N := Character'Pos (C) - Character'Pos ('0');

Re: Characters and Numerics

[Wes Groleau]

Matthew Heaney wrote:
> 
> "M. A. Alves" <maa@liacc.up.pt> wrote in message
> news:mailman.1007554622.31106.comp.lang.ada@ada.eu.org...
> > On 5 Dec 2001, Duke Luke wrote:
> > > How can I change type character to type natural??
> > > e.g: '3' -> 3;
> >
> > Use attribute Value of the type Natural upon a String version of
> > the Character e.g.
> >
> >   N := Natural'Value(C & "");
> 
> Or just
> 
>    N := Character'Pos (C) - Character'Pos ('0');

If C = 'Z' the former will raise constraint error;
the latter will assign N a large number.


-- 
Wes Groleau
http://freepages.rootsweb.com/~wgroleau

Re: Characters and Numerics

[Matthew Heaney]

"Wes Groleau" <wgroleau@usa.com> wrote in message
news:3C0E6D91.43FEE78F@usa.com...
> If C = 'Z' the former will raise constraint error;
> the latter will assign N a large number.

But he stated as a precondition that C is a digit character.  The algorithm
I provided is only guaranteed to satisfy its postcondition if the
precondition is satisfied.

Re: Characters and Numerics

[Wes Groleau]

Matthew Heaney wrote:
> But he stated as a precondition that C is a digit character.  The algorithm
> I provided is only guaranteed to satisfy its postcondition if the
> precondition is satisfied.

Oh, I didn't notice that precondition.  Anyway,
I think one 'value is cleaner than two 'pos and
a subtraction.  Especially if (wild guess) he's
trying to handle multiple digits and doesn't
know he can do one 'value on the whole string.  :-)

-- 
Wes Groleau
http://freepages.rootsweb.com/~wgroleau

Re: Characters and Numerics

[tmoran]

> >   N := Natural'Value(C & "");
>
> Or just
>
>    N := Character'Pos (C) - Character'Pos ('0');

or
  Digit_Value : constant array(Character range '0' .. '9') of Natural
    := (0,1,2,3,4,5,6,7,8,9);
  ...
  N := Digit_Value(C);