dev-cpp-users

[Dev-C++] The & in a conditional statement.

[Daniel G. <sp...@ho...>]

Hi, I'm using the Half Life SDK and am confused by the ampersand symbol, can 
anyone explain what's happening please?

inline BOOL HasConditions( int iConditions ) { if ( m_afConditions & 
iConditions ) return TRUE; return FALSE; }

I also notice we have return TRUE; return FALSE; I'm assuming this is 
perfectly valid as in

if (condition)
   return TRUE;

// if condition was true we would have exited by now.
   return FALSE;

This isn;t relating to HL, it's just a general question about the 
conditional statement. Is it something to do with bit masking?





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Re: [Dev-C++] The & in a conditional statement.

[<cg...@wo...>]

It's performing the logical AND operation with m_afConditions and 
iConditions, if the result is different from zero (true) return true, 
else return false. (Notice that would be shorter do [...]{return 
m_afConditions & iConditions;})
To be true at least one of the bits which is set in m_afConditions has 
to be in iConditions.
AND true table:
1 AND (&) 1 = 1 (true)
1 AND (&) 0 = 0 (false)
0 AND (&) 1 = 0 (false)
0 AND (&) 0 = 0 (false)

Daniel Glenfield wrote:

> Hi, I'm using the Half Life SDK and am confused by the ampersand 
> symbol, can anyone explain what's happening please?
>
> inline BOOL HasConditions( int iConditions ) { if ( m_afConditions & 
> iConditions ) return TRUE; return FALSE; }
>
> I also notice we have return TRUE; return FALSE; I'm assuming this is 
> perfectly valid as in
>
> if (condition)
>   return TRUE;
>
> // if condition was true we would have exited by now.
>   return FALSE;
>
> This isn;t relating to HL, it's just a general question about the 
> conditional statement. Is it something to do with bit masking?
>
>
>
>
>
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Re: [Dev-C++] The & in a conditional statement.

[Zodiaq <zo...@ac...>]

Hello Daniel and all Dev-C++ users,

Saturday, April 26, 2003, 5:34:24 PM, Daniel wrote as follows:

DG> Hi, I'm using the Half Life SDK and am confused by the ampersand symbol, can 
DG> anyone explain what's happening please?

DG> inline BOOL HasConditions( int iConditions ) { if ( m_afConditions & 
DG> iConditions ) return TRUE; return FALSE; }

DG> I also notice we have return TRUE; return FALSE; I'm assuming this is 
DG> perfectly valid as in

DG> if (condition)
DG>    return TRUE;

DG> // if condition was true we would have exited by now.
DG>    return FALSE;

DG> This isn;t relating to HL, it's just a general question about the 
DG> conditional statement. Is it something to do with bit masking?

Yeah, look at this simple sample (I used something very similar in
PHP):

unsigned int uiTypeA = 1; //bits: 00000001
unsigned int uiTypeB = 2; //bits: 00000010
unsigned int uiTypeC = 4; //bits: 00000100
unsigned int uiTypeD = 8; //bits: 00001000

unsigned int uiTypeAC = uiTypeA | uiTypeC; // == 5,bits: 00000101

and now checking:
//uiTepeNew
if( uiTypeNew & uiTypeA )//is bit 00000001 set??
  ;//do something here
if( uiTypeNew & uiTypeB )//is bit 00000010 set??
  ;//do something here

if( uiTypeNew & uiTypeA and uiTypeNew & uiTypeB )//are bits one and two set??
  ;//do some...
and this is something very different:
if( uiTypeNew & uiTypeAB )
  ;//do some...

which means if one (or both) of uiTypeA or uiTypeB set?? This is like
logical OR, and equal to:
if( uiTypeNew & uiTypeA or uiTypeNew & uiTypeB )
  
this bit feauture might be used to send few options (type yes/no) in
one variable... sometimes VERY USEFUL - use only if needed, don't
force it into your progs...
-- 
regards, Zodiaq