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Fabio V Silva wrote: You would think people would at least read it to confirm what they are saying if they are trying to disprove someone...
I confirm before posting anything, check my reply.
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As I have stated in my reply to Fabio, & and && are for different purpose. & is a bitwise operator and && is a logical operator, they may produce same output in certain situations, but it does not mean that you can use them interchangeably. In C#, logical operators always short-circuit.
See this link for an example:
http://blog.dmbcllc.com/2009/03/16/vs-and-vs-whats-the-difference/[^]
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The && operator should be used instead of the & operator for clarity's sake because its the standard way of doing things. Also the && operator gives you some type safety that the & operator does not when dealing with LOGICAL ANDS: (4 && 5) will not compile but (4 & 5) will. If you are intending to perform a LOGICAL AND operation you could end up performing a LOGICAL BITWISE AND operation instead by mistake.
But in any case, the reason you are giving:
"(...)In C#, logical operators always short-circuit(...)
is so wrong I dont even know where to begin.
The operator & is an overloadable operator. Integral and boolean types have their own predefined & binary operators: &(int, int) computes the logical bitwise AND of its operands while &(bool, bool) computes the logical AND of its operands; that is, the result is true if and only if both its operands are true.
This is all straight from the C# specifications:http://msdn.microsoft.com/en-us/library/sbf85k1c.aspx[^]
So bool & bool is NOT A BITWISE OPERATION at all. Its a normal LOGICAL AND OPERATION where both terms are always evaluated contrary to bool && bool where the second term is evaluated if and only if the first term is true.
modified on Thursday, May 19, 2011 5:55 AM
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Ha, that's what they taught me as well. It's utter nonsense off course since both '&' and '|' would be completely useless if that was the only difference.
It's just that it's a good habit to always use '&&' and '||' unless you need '&' or '|' specifically, even in cases where the result is the same.
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This should really mess with your noggin:
bool isTrue = true || true && false;
bool isFalse = true | true && false;
Also, given your example, I'd prefer the double ampersand for 2 reasons: 1) for short-circuiting and 2) for standards' sake.
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I was just discussing the case that someone said that line was incorrect and downvoted my answer when in reality I just copied the OP's line and changed the = to == which is what was actually stopping it from working as expected.
I prefer the double ampersand as well as a standard, the same way I always try to use short circuiting in VB which doesn't seem to be common practice, at least in online samples and articles.
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Ahem!
The real Hall of Shame is the lack of brackets - pure laziness without realizing a simple misstyping mistiping mistyping can change the behaviour of code.
...most people are not a programming god who knows all precedence rules!
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In the case you have posted the final result would be the same as if you had used the && operator. There is, however, an important difference between & and &&. Have a look at this example:
ICollection col = null;
if (col != null && col.Count > 0)
This would first check this expression: col != null; like it is false and we are using && operator, it would not even try to check the second operand, becouse the final result will be false. However, if we use just the bitwise & operator:
ICollection col = null;
if (col != null & col.Count > 0)
Since & operator is a bitwise operator it will try to check both operands so, in this case, it would throw a NullReferenceException when trying to evaluate the result of the second operand. That is why we always use the && operator in our boolean expressions, placing each operand in the right place. I guess this is what others have been trying to explain to you in this thread.
That said, I would not have downvoted your answer just for this if the rest of the answer is correct, and I think that not being able to make you understand this is not reason enough to tell them to RTFM.
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Again, what makes you think I don't know the difference between & and &&?!
I never said they do the same thing and I do know that && is the most commonly used. That, however, does not make it wrong to use & between two boolean and it does not invalidate the fact that in that case it makes no difference. And if someone says it does then they should RTFM!
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Fabio V Silva wrote: what makes you think I don't know the difference between & and &&?!
Oh, nothing at all but, you know, this is a public forum, and although there are many posts in this thread none of them was giving a good explanation about the differencies between those operators, becouse there are differencies, I know them, you know them and I know you know them, but a beginner might get confused after reading this thread. That's all.
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forget it Keith, it's not gonna make any difference, I'm afraid you've just opened a can of worms.
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Fabio V Silva wrote: in that case it makes no difference
Wrong. Take notes if you like:
A && B
In this scenario A is evaluated and if it is true then B is evaluated and that is the result, otherwise the result is false and B never gets evaluated.
A & B
Both A and B are evaluated and the values are then combined using a Bitwise And operation, the output of which is cast to a Boolean for the result.
At any level, these are two very diferent operations.
Fabio V Silva wrote: And if someone says it does then they should RTFM!
Manual read and understood, I still says it does.
Panic, Chaos, Destruction.
My work here is done.
or "Drink. Get drunk. Fall over." - P O'H
OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre
Have a bit more patience with newbies. Of course some of them act dumb -- they're often *students*, for heaven's sake. -- (Terry Pratchett, alt.fan.pratchett)
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Jesus, why do people pretend to know the absolute truth about things without even bothering to do some minimal research.
What you are stating is completely wrong.
The & operator is an OVERLOADABLE operator. As such, it has predefined behaviours for integral types and boolean types.
(int & int) IS NOT THE SAME AS bool & bool. The first performs a logical bitwise AND operation while the latter performs a LOGICAL AND operation. There is no bitwise operation at all if the operator is dealing with two booleans. It is exactly the same as bool && bool except that both terms are evaluated no matter what the first expression evaluates to.
If you are not convinced then please read the following MSDN C# reference link: http://msdn.microsoft.com/en-us/library/sbf85k1c.aspx[^] or better yet: http://msdn.microsoft.com/en-us/library/2a723cdk.aspx[^]
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Come on, guys. Stop this mess, ok? I don't pretend to know the absolute truth about this but, man, you are wrong or, at least, you might be confusing beginners.
The fact that, as you say, "both terms are evaluated no matter what the first expression evaluates to" with the & operator is the key, and it is not a trivial difference. See this example:
string s = null;
bool b1 = s != null && s.Length == 0;
bool b2 = s != null & s.Length == 0;
You see the operands here are boolean expressions. However, while b1 would be assigned false without any problem, a runtime NullReferenceException would be thrown when trying to assing the value to b2. This is a really important difference. Both operands are not the same and can never be considered as if they were the same. Under some circumstances they can return the same result, yes, but that does not mean that they are exactly the same or that you can use any of them when you use boolean expressions.
Can we, please, go on with our lifes now?
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Gets my five - nicely argued.
Real men don't use instructions. They are only the manufacturers opinion on how to put the thing together.
Manfred R. Bihy: "Looks as if OP is learning resistant."
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I'm just a novice programmer and didn't even realize (or I forgot?) that & was a legal command. I've always just used &&. I'm so confused by the last 30 some posts, I'm going to keep it simple and make sure I never use &.
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Wise decision!
Real men don't use instructions. They are only the manufacturers opinion on how to put the thing together.
Manfred R. Bihy: "Looks as if OP is learning resistant."
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Agreed! That is of course only if he meant to say: "I'll never use & with boolean operands." 
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That's how I read it.
Real men don't use instructions. They are only the manufacturers opinion on how to put the thing together.
Manfred R. Bihy: "Looks as if OP is learning resistant."
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Indeed. & and | on ints (or uints) is very useful.
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Absolutely, because && and || wouldn't work with ints (and uints).
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Well f. me sideways and call me Dr Dream. You come and tell me that I don't know what I'm saying and immediately say what I said.
Bitwise means EVERYTHING is evaluated and then anded ored noted xored and stuck through the mincer. Binary menas once the result is known it stops. I appologise if using technical terms confussed you but that's it.
Panic, Chaos, Destruction.
My work here is done.
or "Drink. Get drunk. Fall over." - P O'H
OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre
Have a bit more patience with newbies. Of course some of them act dumb -- they're often *students*, for heaven's sake. -- (Terry Pratchett, alt.fan.pratchett)
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Shut the f... up.
Ego non sum semper iustus tamen Ego sum nunquam nefas!
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So if I have this straight, in your example:
if(UsernameTextBox.Text == "Manager" & PasswordTextBox.Text == "Maintenance")
because both arguments are boolean, the '&' is effectively acting just like a '&&' except for being trivially less efficient because it is always doing both of the string compares.
I know in this case you were merely quoting previous post using '&', but even if the non-short-circuit behaviour would be useful sometime, I'd avoid it because it just looks wrong to me. We're in a mixed C++/C# environment here, and I have to be on the lookout for misused '&'s in the code as it is. Allowing for false positives is not in the cards here.
That said, I think you got a raw deal.
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