Feel like a dufus... Coding question!

[babywax]

Well I'm 14, started when I was 10, but I think I'm fairly smart for my age... (Not to toot my own horn)

[Commodus]

LOL what a coincidence... I'm 14 as well Started a year ago, though...

 

Some more bitwise operators:

 

The ~ unary operator

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Switches bits which are on off, and ones that are off on. I.e.

 

~1 = 0 (pre: 1, post: 0)

~1010 = 0101 (pre: 10, post: 5)

~11011000 = 00100111 (pre: 216 post: 39)

 

When used with & it's very useful - it allows you to separate sections of bits from a bigger number. For example, if you want to take somebody's lightsaber away, then you would do

 

client->ps.stats[sTAT_WEAPONS] &= ~(1 << WP_SABER);

 

stats[sTAT_WEAPONS] is an array with 16 bits, and each bit represents a weapon. If the bit is on then the player has that weapon; if it's off then he/she doesn't have that weapon. ~(1 << WP_SABER) turns off the bit that corresponds with the saber and turns on all the other ones.

 

If you have the saber, then it turns that bit off (1 & 0 = 0) and all the other bits stay the same, therefore the weapons are retained (if the bit is off, it stays the same: 0 & 1 = 0. if it's on, then 1 & 1 = 0 so nothing changes).

 

The left shift operator <<

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The left shift operator simply shifts the number in binary form one bit position to the left. e.g.

 

00000110 << 3 = 00110000 (pre-shift: 6, post-shift: 96)

00000001 << 1 = 00000010 (pre-shift: 1, post-shift: 2)

 

It's the same as multiplying the number by 2 to the power of the number of positions shifted left.

 

The right shift operator >>

-------------------------------------

 

The right shift operator, like the left shift operator, shifts the number in binary form one bit position to the right, e.g.

 

00000110 >> 1 = 00000011 (pre-shift: 6, post-shift: 3)

11110000 >> 4 = 00001111 (pre-shift: 240 post-shift: 15)

 

If you keep shifting and there isn't a position for the bit to move into it simply disappears. So

 

00000110 >> 2 = 00000001 (pre-shift: 6, post-shift: 1)

 

It's the same as as dividing the number by 2 to the power of the number of positions shifted right (except when there are no spaces left).

 

It's useful when you want to get rid of a portion of a number that you don't need. I can't think of a specific example at the top of my head but I'm sure there are some.

 

Bitwise excusive OR ^:

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It's the same as | but if the corresponding bits are both 1, then the result is 0.

 

Logic:

0 ^ 0 = 0

0 ^ 1 = 1

1 ^ 0 = 1

1 ^ 1 = 0

 

Example:

1110 ^ 0011 = 1101

1000 ^ 1001 = 0001

 

Can't think of where you can use this either, but there are probably some situations... otherwise it wouldn't have been added to C, wouldn't it?

 

Hope this helps,

Commodus

[ET Warrior]

Well, I've been programming for two years, unfortunately the only language my school offers is visual basic.....which is pretty much really crappy.......I rather don't like visual basic. But I have been trying to teach myself C++ for the past couple of weeks, so hopefully I won't have too hard of a time next year in college

[recombinant]

Originally posted by wudan

I mean ... it's me, razorace, JediStone should be back soon, Commodus has been known to appear there ... you know.

 

...resurfacing presently!!!

 

[Wudan]

** blinks **

 

I have seen a ghost!

[Commodus]

Wudan - go on #jk2coding @ irc.quakenet.org! The power of Christ compells you!

[Wudan]

Well, I went, but you were IDLE.

 

Thx A loT.

[Commodus]

Ooops. Sorry about that. I live in Hong Kong in China, so around the time you go online I go to sleep. There was a football match between Man U. and Real Madrid on at 2:30 in the morning so I thought I could go for sleep for 3 hours (this was at 11:00 at night) then get up again at 2, chat on #jk2coding and watch the game and do both at the same time. Only problem was I couldn't be woken up from my sleep. Sorry