Re: string operations

[Jeff Carter <jrcarter@acm.org>]

Margit Gut wrote:
> I try to read a string from the keyboard and then I want to write a
> recursiv function to turn the characters  from the end to the beginning.

The requirement that this be a recursive function sounds like a homework
problem.

> 
> I fetch the string with Get_Line. I declared the string with
> Sstring : string(1..255);
> So whatever I try, the string'Length is always 255.

Given the declaration

S : String (1 .. 255);

S'Length is always 255. This is the definition of the 'Length attribute
on an array object.

Look carefully at the description of Get_Line in the ARM (A.10.7),
especially the meaning of the Last parameter, and then read about slices
(ARM 4.1.2). You can find the ARM on line at

http://www.adapower.com/rm95/index.html

If the string read by Get_Line is shorter than its Item parameter, it is
stored in Item (Item'First .. Last). Thus, after executing

Get_Line (Item => S, Last => Last);

the string of interest is in the slice

S (S'First .. Last)

>  My next poblem is, how to do a correct Function, that calls itselve.

A function calls itself exactly the same way that any other statement
calls the function:

function F (N : Positive) return Positive is
begin -- F
   if N <= 1 then
      return N;
   else
      return N * F (N - 1);
   end if;
end F;

-- 
Jeff Carter
"You tiny-brained wipers of other people's bottoms!"
Monty Python & the Holy Grail