strange effect: if ... else in C influence a previous statement Post: 302260273

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Top Forums Programming strange effect: if ... else in C influence a previous statement Post 302260273 by cdbug on Thursday 20th of November 2008 04:31:04 AM

11-20-2008

Registered User

strange effect: if ... else in C influence a previous statement

I write a short code in c

it may work well, but when I add an if ... else ... structure, a computation before the structure can not give a correct result

compilation and run can do well, but the result is wrong. Very strange

(1)
y2 = expression; //y2 = 0 always 0 error
.................

add : if(a->is_root) c = m2 - y2;
else f = m2 - y2;

(2)

y2 = expression; //y2 = 0 always 0 error
.................

add : if(a->is_root) c = m2 - y2;
if(!a->is_root) f = m2 - y2;

(3)
y2 = expression; // y2 = normal value; normal
.................

add : //if(a->is_root) c = m2 - y2;
if(!a->is_root) f = m2 - y2;

(4)

y2 = expression; // y2 = normal value; normal
.................

add : if(a->is_root) c = m2 - y2;
//if(!a->is_root) f = m2 - y2;

(5)
y2 = expression; // y2 = normal value; normal

add : //if(a->is_root) c = m2 - y2;
//if(!a->is_root) f = m2 - y2;

Trouble: can not use if... else ... normally

Question: (1) if... else ... can influence a previous statement, why?
(2) How to solve the problem?

Last edited by cdbug; 11-20-2008 at 05:38 AM..

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LEARN ABOUT OSX

ppi::statement::null

PPI::Statement::Null(3) 				User Contributed Perl Documentation				   PPI::Statement::Null(3)

NAME

       PPI::Statement::Null - A useless null statement

SYNOPSIS

	 my $foo = 1;

	 ; # <-- Null statement

	 my $bar = 1;

INHERITANCE

	 PPI::Statement::Null
	 isa PPI::Statement
	     isa PPI::Node
		 isa PPI::Element

DESCRIPTION

       "PPI::Statement::Null" is a utility class designed to handle situations where PPI encounters a naked statement separator.

       Although strictly speaking, the semicolon is a statement separator and not a statement terminator, PPI considers a semicolon to be a
       statement terminator under most circumstances.

       In any case, the null statement has no purpose, and can be safely deleted with no ill effect.

METHODS

       "PPI::Statement::Null" has no additional methods beyond the default ones provided by PPI::Statement, PPI::Node and PPI::Element.

SUPPORT

       See the support section in the main module.

AUTHOR

       Adam Kennedy <adamk@cpan.org>

COPYRIGHT

       Copyright 2001 - 2011 Adam Kennedy.

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

       The full text of the license can be found in the LICENSE file included with this module.

perl v5.16.2							    2011-02-25						   PPI::Statement::Null(3)