Anyway to change the length of a string ?

Anyway to change the length of a string ?

[Jim]

.... after you have already declared it before BEGIN ?

i am making a Hangman game with words up to 10 letters long.

now i declare a string which would be used in the program for the word
which can be 1-10 letters.

so i say

s : string(1..10)


but in the program i cant say

s:= "hello"

because 's' has to be 10 characters long right ?

can i have it so i can change the length of 's' from 10 char to 5
characters in the program and then input the value as "hello" ?

thanks

Re: Anyway to change the length of a string ?

[David C. Hoos]

Use the package Ada.Strings.Unbounded or
Ada.Strings.Bounded instead of using fixed-length strings.

----- Original Message ----- 
From: "Jim" <genx54321@hotmail.com>
Newsgroups: comp.lang.ada
To: <comp.lang.ada@ada.eu.org>
Sent: Wednesday, August 14, 2002 2:56 PM
Subject: Anyway to change the length of a string ?


> .... after you have already declared it before BEGIN ?
> 
> i am making a Hangman game with words up to 10 letters long.
> 
> now i declare a string which would be used in the program for the word
> which can be 1-10 letters.
> 
> so i say
> 
> s : string(1..10)
> 
> 
> but in the program i cant say
> 
> s:= "hello"
> 
> because 's' has to be 10 characters long right ?
> 
> can i have it so i can change the length of 's' from 10 char to 5
> characters in the program and then input the value as "hello" ?
> 
> thanks
> _______________________________________________
> comp.lang.ada mailing list
> comp.lang.ada@ada.eu.org
> http://ada.eu.org/mailman/listinfo/comp.lang.ada
> 

Re: Anyway to change the length of a string ?

[Stephen Leake]

genx54321@hotmail.com (Jim) writes:

> .... after you have already declared it before BEGIN ?
> 
> i am making a Hangman game with words up to 10 letters long.
> 
> now i declare a string which would be used in the program for the word
> which can be 1-10 letters.
> 
> so i say
> 
> s : string(1..10)
> 
> 
> but in the program i cant say
> 
> s:= "hello"

You can say 

S (1 .. 5) := "hello";

or

S := "hello" & "     ";

> because 's' has to be 10 characters long right ?
> 
> can i have it so i can change the length of 's' from 10 char to 5
> characters in the program and then input the value as "hello" ?

See the standard package Ada.Strings.Unbounded.

-- 
-- Stephe

Re: Anyway to change the length of a string ?

[Warren W. Gay VE3WWG]

Stephen Leake wrote:
 > genx54321@hotmail.com (Jim) writes:
 >>.... after you have already declared it before BEGIN ?
 >>
 >>i am making a Hangman game with words up to 10 letters long.
 >>
 >>now i declare a string which would be used in the program for the word
 >>which can be 1-10 letters.
 >>
 >>so i say
 >>
 >>s : string(1..10)
 >>
 >>but in the program i cant say
 >>
 >>s:= "hello"
 >
 > You can say
 >
 > S (1 .. 5) := "hello";
 >
 > or
 >
 > S := "hello" & "     ";

These are all reasonable solutions.

Expanding upon the above solutions slightly, examine the
following tested piece of code for an example:

with Ada.Text_IO;

procedure EG is
     use Ada.Text_IO;

     function Length(S : String) return Natural is
     begin
        return S'Length;
     end Length;

     S :      String(1..10) := "1234567890";
     Last :   Natural := S'Last;
begin
     Put_Line("S='" & S(1..Last) & "'");

-- Last       := 3; -- or..
     Last       := Length("Cat");  -- Because can't use "Cat"'Last
     S(1..Last) := "Cat";

     Put_Line("S='" & S(1..Last) & "'");

end EG;

The idea is that you work with a variable called Last
(or something like it). If you don't like counting
characters in a larger constant like "Some message..."
then the use of a Lenght() function can be helpful (see
the statement Last := Length("cat");). Unfortunately,
doing "Some very long string constant"'Last is not legal.

At other times, you declare the variable when you
know its length, like:

declare
     My_New_String : String(1..Computed_Length);
begin
     ...

Or you have a function return the exact length string
you need, as in:

declare
     Returned_String : String := My_Function(whatever);
begin
     ...

and then thow it away when you're done with it using:

end;

of the declare..begin..end block. You can do this for
each iteration within a loop as well.

This requires a little different planning than C programmers
are used to. But once you catch onto the general paradigm
shift, you'll find that Ada fixed strings, packages
Ada.Strings.Fixed and Ada.Characters.Handling cover most
of your string needs.

If you deal with a number of variable length strings, then
sometimes resorting to Ada.Strings.Unbounded makes your
life easier as many have already pointed out. However, I
find that once you cross over to Ada.Strings.Unbounded, then
other features of these strings become "less natural" (for
example you must use a Length function instead of a Length
attribute).

Hope this helps, Warren.
-- 
Warren W. Gay VE3WWG
http://home.cogeco.ca/~ve3wwg

Re: Anyway to change the length of a string ?

[tmoran]

> now i declare a string which would be used in the program for the word
> which can be 1-10 letters.
"An object of a particular Bounded_String type represents a String whose
low bound is 1 and whose length can vary conceptually between 0 and a
maximum size established at the generic instantiation."  ARM A.4.4(1)
Sound like what you want?