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Thanks Nigel. I have a serious problem with
the following remark :
> If you leave out the break statements,
and
> _expression_==constant_expression1 you will execute statement1 (what
you
> wanted) AND ALSO
statement2 AND ALSO statement3 AND ALSO ... statementN
> AND ALSO
statement_default.
So what you
are telling me is that after having executed statement1, SWITCH will execute all
the other case statements too. Because there is no break.
I am using the SWITCH ( Visual Foxpro called DO CASE ) statement
and never have seen this. Once one of the cases it true, the corresponding
command will be executed and you're leaving the SWITCH structure. There are no
breaks needed to exit SWITCH. Is this different in AFL ? Please reed
underneath mentioned help text from MS Visual FoxPro
:
CASE lExpression1 Commands ... When
the first true (.T.) CASE _expression_ is encountered, the set of commands
following it is executed. Execution of the set of commands continues until the
next CASE or ENDCASE is reached. Execution then resumes with the first command
following ENDCASE.
If a CASE _expression_ is false (.F.), the set of
commands following it up to the next CASE clause is ignored.
Only one set of
commands is executed. These are the
first commands whose CASE _expression_ evaluates to true (.T.). Any succeeding
true (.T.) CASE expressions are ignored.
Of course what I should and will do is test what
the AFL SWITCH really does ...
Regards, Ton.
----- Original Message -----
Sent: Friday, May 25, 2007 12:12 PM
Subject: Re: [amibroker] Re: Nested Switch()
statements
> On Fri, 25 May 2007, Ton Sieverding wrote:
> > Can you
please explain me why 'switch statements are a frequent
> > source of
bugs' ? If the last CASE is a DEFAULT then all possible
> > cases are
covered. Or am I missing something in the AFL SWITCH
> > statement
?
> >
> > switch ( _expression_ )
> > {
>
> case constant-expression1 : statement;
>
> case constant-expression2 : statement;
>
> ...
> > case
constant-expressionN : statement;
> >
>
> default : statement;
> >
> >
}
> >
> >
> > Ton.
>
> The 'standard'
error when using a switch statement in 'C' and presumably
> AFL, is
forgetting to put 'break;' statements in.
>
> To paraphrase your
example (above) so it looks like this:-
>
> switch ( _expression_
)
> {
> case constant-expression1 :
statement1;
> case constant-expression2 :
statement2;
> ...
> case
constant-expressionN : statementN;
> default :
statement_default;
> }
>
> If you leave out the break
statements, and
> _expression_==constant_expression1 you will execute
statement1 (what you
> wanted) AND ALSO statement2 AND ALSO statement3
AND ALSO ... statementN
> AND ALSO statement_default.
>
>
It's sometimes called the 'fall-through' bug. It's easy to miss, can be
> a right pain!
>
>
> --
> Nigel Rowe
>
rho \N{COMMERCIAL AT} swiftdsl \N{FULL STOP} com \N{FULL STOP} au
>
>
>
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