What's syntax for a case statement?

What's syntax for a case statement?

[Scott B Moore]

I'm new to Ada and I can't find the syntax for a case statement.  Any help?

Re: What's syntax for a case statement?

[John G. Volan]

Scott B Moore wrote:
> 
> I'm new to Ada and I can't find the syntax for a case statement.  Any help?

I would think that any good textbook on Ada would have an index in the
back with an entry on "case statements" directing you to the proper
page. :-)  Are you taking a course on Ada at the University of Buffalo? 
Surely your professor must have assigned you a decent textbook with a
good index! :-)

If for some reason you don't have such a textbook, never fear, you can
consult the online Ada95 Language Reference Manual at

  http://www.adahome.com/rm95/

The immediate answer to your question is in section 5.4:

  http://www.adahome.com/rm95/rm9x-05-04.html

The syntax notation is not altogether impossible to decipher, and there
are a few examples of case statements at the bottom that will give you
the idea.

However, I don't recommend trying to learn Ada from the RM95. It was
designed to be a precise and unambiguous specification of the language,
not a tutorial.  You can find some good online tutorials, textbook
reviews, and many other useful resources at the "Home of the Brave Ada
Programmers" web site:

  http://www.adahome.com/

Good luck to you!

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Re: What's syntax for a case statement?

[Michael F Brenner]

truth: constant boolean := weigh_canopic_jar_against_feather_of_Maat;
...
case truth is
  when true  => fire_of_dispersion.pass;    
  when false => fire_of_dispersion.dissolve;
end case; 

Re: What's syntax for a case statement?

[Darren C Davenport]

Scott B Moore (sbmoore@cs.buffalo.edu) wrote:
: I'm new to Ada and I can't find the syntax for a case statement.  Any help?

http://www.adahome.com/rm95/rm9x-05-04.html

Re: What's syntax for a case statement?

[Alan Brain]

Wolfgang Gellerich wrote:
> 
> In article <5nk6gu$gbp@prometheus.acsu.buffalo.edu>, sbmoore@cs.buffalo.edu (Scott B Moore) writes:
> |> I'm new to Ada and I can't find the syntax for a case statement.  Any help?
> 
> Probably, you will need an introduction/ description of Ada - try "Programming
> in Ada95" by John Barnes.

I agree, it's an excellent book, one I'd highly recommend. I've been
using Barnes' "Programming in Ada" for many years, both to teach, and as
a reference for rarely-used constructs and predefined specifications.

BTW, the syntax is

case < name-of-a-descrete variable> is
  when <selection1> => <sequence of statements>;
  when <selection2>  | <selection3> => <sequence of statements>;
  when <selection4>..<selection5> => <sequence of statements>;
 [when others       => <sequence of statements>;
end case;

Examples:
Assuming you have
type TRAFFIC_LIGHT_TYPE is (Red,Green,Amber);
and a variable
ONCOMING_LIGHTS : TRAFFIC_LIGHT_TYPE;      

then you could have

case ONCOMING_LIGHTS is
  when Red  | Amber => STOP(THE_CAR);
  when Green =>
              if ALREADY_STOPPED(THE_CAR) then
                 START(THE_CAR);
              end if;
end case;

or

case ONCOMING_LIGHTS is
 
  when Green =>
              if ALREADY_STOPPED(THE_CAR) then
                 START(THE_CAR);
              end if;

  when others => STOP(THE_CAR);

end case;

Other examples:
ThisLetter : CHARACTER;

case ThisLetter is
  when 'a'..'z' => CHANGE_TO_UPPERCASE(ThisLetter);
  when others   => null;
end case;

ThisInteger : INTEGER;

case ThisInteger is
  when -37..2 => <sequence of statements>
  when 3 | 5  => <some other sequence of statements>
  when 6      => <yet another sequence of statements>
  when others => <and the default sequence of statements>
end case;

OK? 
-- 
aebrain@dynamite.com.au     <> <>    How doth the little Crocodile
| Alan & Carmel Brain|      xxxxx       Improve his shining tail?
| Canberra Australia |  xxxxxHxHxxxxxx _MMMMMMMMM_MMMMMMMMM
100026.2014 compuserve o OO*O^^^^O*OO o oo     oo oo     oo  
                    By pulling MAERKLIN Wagons, in 1/220 Scale
See http://www.z-world.com/graphics/z/master/8856.gif for picture

Re: What's syntax for a case statement?

[David C. Hoos, Sr.]

Hi Alan,

Just a small nit, but <name-of-a-descrete variable>  in your case statement
syntax definition would be more
nearly correct if it said <discrete-expression>  -- e.g., a function call
returning a discrete value.

David C. Hoos, Sr.,

Alan Brain <aebrain@dynamite.com.au> wrote in article
<33A0B0BE.30A8@dynamite.com.au>...
> Wolfgang Gellerich wrote:
> > 
> > In article <5nk6gu$gbp@prometheus.acsu.buffalo.edu>,
sbmoore@cs.buffalo.edu (Scott B Moore) writes:
> > |> I'm new to Ada and I can't find the syntax for a case statement. 
Any help?
> > 
> > Probably, you will need an introduction/ description of Ada - try
"Programming
> > in Ada95" by John Barnes.
> 
> I agree, it's an excellent book, one I'd highly recommend. I've been
> using Barnes' "Programming in Ada" for many years, both to teach, and as
> a reference for rarely-used constructs and predefined specifications.
> 
> BTW, the syntax is
> 
> case < name-of-a-descrete variable> is
>   when <selection1> => <sequence of statements>;
>   when <selection2>  | <selection3> => <sequence of statements>;
>   when <selection4>..<selection5> => <sequence of statements>;
>  [when others       => <sequence of statements>;
> end case;
> 
> Examples:
> Assuming you have
> type TRAFFIC_LIGHT_TYPE is (Red,Green,Amber);
> and a variable
> ONCOMING_LIGHTS : TRAFFIC_LIGHT_TYPE;      
> 
> then you could have
> 
> case ONCOMING_LIGHTS is
>   when Red  | Amber => STOP(THE_CAR);
>   when Green =>
>               if ALREADY_STOPPED(THE_CAR) then
>                  START(THE_CAR);
>               end if;
> end case;
> 
> or
> 
> case ONCOMING_LIGHTS is
>  
>   when Green =>
>               if ALREADY_STOPPED(THE_CAR) then
>                  START(THE_CAR);
>               end if;
> 
>   when others => STOP(THE_CAR);
> 
> end case;
> 
> Other examples:
> ThisLetter : CHARACTER;
> 
> case ThisLetter is
>   when 'a'..'z' => CHANGE_TO_UPPERCASE(ThisLetter);
>   when others   => null;
> end case;
> 
> ThisInteger : INTEGER;
> 
> case ThisInteger is
>   when -37..2 => <sequence of statements>
>   when 3 | 5  => <some other sequence of statements>
>   when 6      => <yet another sequence of statements>
>   when others => <and the default sequence of statements>
> end case;
> 
> OK? 
> -- 
> aebrain@dynamite.com.au     <> <>    How doth the little Crocodile
> | Alan & Carmel Brain|      xxxxx       Improve his shining tail?
> | Canberra Australia |  xxxxxHxHxxxxxx _MMMMMMMMM_MMMMMMMMM
> 100026.2014 compuserve o OO*O^^^^O*OO o oo     oo oo     oo  
>                     By pulling MAERKLIN Wagons, in 1/220 Scale
> See http://www.z-world.com/graphics/z/master/8856.gif for picture
> 
> 
> 

Re: What's syntax for a case statement?

[Robert Dewar]

Alan said

<<case < name-of-a-descrete variable> is
  when <selection1> => <sequence of statements>;
  when <selection2>  | <selection3> => <sequence of statements>;
  when <selection4>..<selection5> => <sequence of statements>;
 [when others       => <sequence of statements>;
end case;
 >>


This is completely wrong, there is no requirement that the expression after
the case be the name of a discrete variable, it is a general expression.

If you are going to post syntax that can easily be looked up, at least do
it right!

Also, your style of using examples, rather than proper syntax, for the
when phrases is also confusing. It is hard to understand for example
that it is fine to have

when x | y .. z =>

Re: What's syntax for a case statement?

[Alan Brain]

Robert Dewar wrote:
> 
> Alan said
> 
> <<case < name-of-a-descrete variable> is

> This is completely wrong, there is no requirement that the expression after
> the case be the name of a discrete variable, it is a general expression.
> 
> If you are going to post syntax that can easily be looked up, at least do
> it right!

I stand corrected, and my thanks.

Moral of story: Never, ever, post on a public newsgroup at 3 am,
immediately after writing to a student why he couldn't say

case NameOfAFloat is
  when 0.0..3.768 =>

 
-- 
aebrain@dynamite.com.au     <> <>    How doth the little Crocodile
| Alan & Carmel Brain|      xxxxx       Improve his shining tail?
| Canberra Australia |  xxxxxHxHxxxxxx _MMMMMMMMM_MMMMMMMMM
100026.2014 compuserve o OO*O^^^^O*OO o oo     oo oo     oo  
                    By pulling MAERKLIN Wagons, in 1/220 Scale
See http://www.z-world.com/graphics/z/master/8856.gif for picture

Re: What's syntax for a case statement?

[Robert Dewar]

<<Moral of story: Never, ever, post on a public newsgroup at 3 am,
immediately after writing to a student why he couldn't say
>>

Well anyone can get syntax wrong at 3 am, although amazingly enough
GNAT seems to diagnose syntax errors at any time of day fearlessly :-) :-)