Just confirming, is comparison 1 evaluating to comparison 2 or 3?
Code:int a = 0, b = 0, c = 0, d = 0;
//Comparison 1
if(a == b == c)
{
d++;
}
//Comparison 2
bool res = a == b;
if(res == c)
{
d++;
}
//Comparison 3
if(a == b &&
b == c)
{
d++;
}
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Just confirming, is comparison 1 evaluating to comparison 2 or 3?
Code:int a = 0, b = 0, c = 0, d = 0;
//Comparison 1
if(a == b == c)
{
d++;
}
//Comparison 2
bool res = a == b;
if(res == c)
{
d++;
}
//Comparison 3
if(a == b &&
b == c)
{
d++;
}
First off, comparisons don't evaluate to one another, they evaluate to a bool result. So I suppose you're simply asking whether they all have the same result.Quote:
Originally Posted by ahmd
In #1 I'm not 100% sure about the evaluation sequence mandated by the standard, but that doesn't matter either: In the end you're comparing the result of an equality comparison between two equal ints (i.e. true) with a third int that's 0. Since true is converted to a non-zero integer (usually 1, but I don't think that's mandatory, but any non-zero value would lead to the same result) the final result is true.
In #2 you're enforcing a certain evaluation sequence by assigning an intermediate result to a temporary variable, but aside from this it essentially is the same as #1.
#3 is obvious, isn't it? ;) You're comparing 0 and 0 for equality twice. The comparison evaluates to true in both cases, so the && eventually will evaluate to true as well.
However, I don't see what that has to do with Win API. Could it be that you were one off when clicking the section you wanted to post that in? ;)
It said, "C++ and WinAPI", so I'm taking it as C++ (since there's no C section here). If it's a wrong section, I'll let moderator move it.
Going back to my question. I'm not asking about all three situations. I'm asking about comparison #1 and what it evaluates to. And no, your assumption is not correct. The first if statement will result in a false.
C++ precedence rules aren't Windows API issues.Quote:
Originally Posted by ahmd
http://www.cppreference.com/wiki/lan...tor_precedence
a == b is true. ThenQuote:
The first if statement will result in a false.
is false, since c is 0, so the entire expression is false.Code:true == c
Regards,
Paul McKenzie
Quote:
Originally Posted by ahmd
D'oh! That's what happens when I make conclusions too quickly... :blush:Quote:
Originally Posted by Paul McKenzie
But, ahmd, if you already knew that, why then did you ask? :confused: Did you intend to test us? :ehh:
I'm trying to save myself coding time. If you look at the mathematical sense, a == b == c should evaluate to "if 'a' equals 'b' and 'b' equals 'c'", which is not the case for if(a == b == c) statement.
Hmmm... Didn't you learn something from all the threads you probably have read here during the last two years? How many times have you seen something like this in a beginner's program:
This obviously won't work: Programming languages (maybe except some experimental ones) don't understand everyday's language used in inter-human communication.Code:if (answer == 'y' || 'n')
What you are trying may be seen as a bit less daring since you're "just" trying to make C++ understand some common math jargon idioms. Eventually, however, this won't work either, simply because that's not part of the C++ language. (The language does have these "chained assignments" which look pretty similar but actually are something completely different.)
Chances are that you actually may find a language that understands this, but of course this will not be C++ and so you have to abandon C++ and make a migration. Also, perhaps this language understands your simplified syntax but produces slower code. Are you really willing to save a few keystrokes at the expense of the efficiency of your final program? ;)
C is not a mathematician's language, that's what you should keep in mind at coding time. This habit will save your debugging time which cost is much bigger than coding time.Quote:
Originally Posted by ahmd
Wow, thank you for your condescending replies.
I'm not trying to learn the C++ language, I was simply asking about that specific construct. What shook me is that normally VC compiler gives you a warning if you write something like if(a = 1) but not in this case...
Not mine.
Is a perfectly valid statement. There are many times I do something like:Code:if (a = 1)
Also,Code:if (bQuit = SomeFuncCall())
{
// Do more stuff here
}
is valid as well. As already stated, this will be evaluated left to right, returning "false" in your example.Code:if (a == b == c)
Viggy
I always get surprised how other people are able to find condescension in a trivial reply to a trivial question with an obvious answer. Does it sound condescending to say 'think in French when you write in French'?Quote:
Originally Posted by ahmd
If you had a warning thing as a main point, why did you talk about mathematical notation? Don't you find this a bit confusing? ;)Quote:
I'm not trying to learn the C++ language, I was simply asking about that specific construct. What shook me is that normally VC compiler gives you a warning if you write something like if(a = 1) but not in this case...
BTW, it shake me every time how easily you get excited by the things I'd never even notice, or paid really less attention.
You might be right. I think I had a bad day yesterday. It all actually started in another thread when people were treating me like some noob programmer... I guess there are quite a few of them here.
Well, you're definitely not a noob, so why to bother about what others say or think of you. Being positive about yourself is a great thing, almost the same great as being demanding to yourself and forgiving to others. :)
Wow, I didn't know I'd get this kinda encouragement on this site :) It was just too many things going wrong at once... I'm sure you've experienced that... anyway, thanks.
[ Moved thread ]Quote:
Originally Posted by ahmd
That's not exactly what happened. You mentioned a crash and gave no code and no context. I'm not really sure what you expected.Quote:
Originally Posted by ahmd
parentheses are free!
How does adding parentheses help?Quote:
Originally Posted by deyili
Evaluates to the false, just as before.Code:if (a == (b == c))
Viggy
Wouldn't if((a==b) && (b==c)) work for a true outcome?
Yes, it would. That's how it should've been coded anyway.Quote:
Originally Posted by ElectricCash
Yes, but now you're changing the condition. You're not just adding parens.Quote:
Originally Posted by ElectricCash
Viggy
ElectricCash, you see, the reason I started this thread is because it was somewhat confusing to me when I came across that double equation comparison statement. I have an experience of well over 15 years with C/C++ and I was thrown off by it, I should admit. What made it confusing for me is a mathematical notation (that involves the use of the AND operator in its logic) which is not the case for the way that statement is evaluated in C. Again, I'm not arguing with C/C++ standards -- we cannot change them from here -- but in my book a compiler should issue a warning when such statement is encountered, since clearly, if a, b and c are all int's comparing a boolean (which is the result of the first comparison) to an int, although possible, makes little sense. Again, this is my opinion and I learned my lesson.
Hmmm, yeah. I would have expected something like this:
However, this warning only trips on this 'if' stmt:Code:1>d:\projects\junkconsole\test.cpp(15) : warning C4805: '==' : unsafe mix of type 'bool' and type 'int' in operation
ViggyCode:bool res = a == b;
if(res == c)
{
d++;
}
I suspect that for legacy C compatibility reasons, primitive comparisons actually return int rather than bool.
I doubt that.Quote:
Originally Posted by Lindley
Code:int a = 0;
int b = 1;
int c = sizeof(a == b); //VS2008: c = 1
int d = sizeof(int); //VS2008: d = 4
Did you compile as a 'C' file or CPP? 'C' and C++ have different language rules, so I would suspect that the same code would produce sizeof(int) for the comparison.Quote:
Originally Posted by ahmd
Regards,
Paul McKenzie
Maybe. I'll let someone else try it out. I stopped using C... oh boy, 10+ years ago.... maybe more. The only reference to C I get these days is when dealing with Objective-C (OSX/iOS).Quote:
Originally Posted by Paul McKenzie
I'm not sure what the standard says about this. I'm just wondering about the reason for the particular compiler not throwing the warning.Quote:
Originally Posted by ahmd
There's a command line switch for the Visual Studio compiler to compile a particular source file as a 'C' file. Or, if on Linux, just use 'gcc' (instead of 'g++').Quote:
Originally Posted by ahmd
Viggy