CODEWITHSUNDEEP
coding-style
Bill B
Bill B

Reputation: 1300

negated equal vs. not equal

Lately, I've been reading some code that has 

 if (! (a == b) )

instead of 

 if ( a != b )

in some places.

Obviously these are logically equivalent, but I'm wondering if there is any particular reason to use one over the other.

Are there certain circumstances where one is preferable, or is it all just a matter of personal style?

Upvotes: 4

Views: 1291

Answers (7)

MRFerocius
MRFerocius

Reputation: 5629

This is the DeMorgan theorem. (Augustus De Morgan - Mathematician)

Go for if(a != b)

Upvotes: -5

bgiles
bgiles

Reputation: 1220

Any half-way decent compiler will put out the same code (unless == and != have been overloaded, as mentioned elsewhere) so optimization questions are irrelevant.

I don't think I've ever seen "if(!(a==b))" outside of a bigger conditional where it is clearer to not use DeMorgan's theorem, but I guess I could see it as a way of emphasizing that the two values really should be identical and there's something deeply wrong if they're not. However a honking big "throw OmgICantBelieveThisHappenedException()" on the next line would be even clearer. :-)

Other than these two situations I have to agree with the "use !=" camp since it's clearer when you skim the code. The '!' can be easily overlooked, especially with some formatting conventions.

Upvotes: 1

Stefan Kendall
Stefan Kendall

Reputation: 67822

As mentioned, languages with operator overloading often don't enforce a != for every ==. In this case, !( a == b ) is essential, as a != b is undefined. Furthermore, it may make sense in context to use !( a == b ). While the shorter form is preferred for the reasons given elsewhere in this question, the lengthier form can be more descriptive in certain problem sets.

Upvotes: 4

Seb
Seb

Reputation: 25147

I really prefer

if ( a != b )

simply because you are supposed to read less and you understand more quickly the message the programmer wanted to transmit.

Remember programmers spend more time reading code than writing it, so the more you can do to make code more understandable, the better.

Upvotes: 13

mP.
mP.

Reputation: 18266

Your code should be as simple as possible, ie less statements is better thus the a!=b is 3 constructs as opposed to ! (a=b) which is 4.

Upvotes: 1

John Dibling
John Dibling

Reputation: 101456

Mostly this is a matter of style (and my preference is for 'a != b'), but there could be an actual difference in operation if a is an object of a class that doesn't have either an operator== or an operator!=.

Upvotes: 9

Bill the Lizard
Bill the Lizard

Reputation: 405755

I would avoid

if (! (a == b) )

since it involves two operations, where there is one operator

if ( a != b )

that does the exact same thing. The second is also more readable (if only slightly).

The really big problem I have with

if (! (a == b) )

is that it made me stop and think "what the heck?" Good code shouldn't do that.

Upvotes: 6

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