Is there a difference between i==0 and 0==i?

Question

First code:

  if(i==0) {// do instructions here}

Second code:

  if(0==i) { // do instructions here }

What is the difference between the blocks?

One won't have you spending time debugging because you forgot a `=`. — alex, May 18 '12 at 16:33
You're at least safe from the `if (i=0) {}` problem if you're using c#, since that syntax is illegal. — Chris Farmer, May 18 '12 at 16:35
@KendallFrey it is a valid expression in C++, so there is nothing for the compiler to catch. — juanchopanza, May 18 '12 at 16:37
And yet, @Juan, some C++ compilers catch it anyway. There it's a quality-of-implementation issue. — Rob Kennedy, May 18 '12 at 16:38
If you overloaded the == operator (not possible in all listed languages) you could make A == B different from B == A (not that you *should*, but you *can*). — Servy, May 18 '12 at 16:58
reopened - the linked duplicate was weak, and this question has a good answer — M.M, Jun 18 '15 at 15:32

Alok Save · Accepted Answer · 2012-05-19T14:30:54.670

32

Functionally, there is no difference.
Some developers prefer writing the second format to avoid assignment typos(in case you miss a =), so that compiler warns of the typo.
The second is famously known as Yoda Condition.

Yoda Condition

I say there is no difference because, you cannot guard yourself against every minuscule detail and rely on compiler to cry out aloud for you.If you intend to write a == you should expect yourself to write a == and not a =.
Using the second format just leads to some obscure non-readable code.
Also, most of the mainstream compilers warn of the assignment instead of equality typo by emitting an warning once you enable all the warnings(which you should anyways).

edited May 19 '12 at 14:30

answered May 18 '12 at 16:34

Alok Save

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Its too bad they didn't put a historical lock on the [jargon question](http://stackoverflow.com/questions/2349378/new-programming-jargon-you-coined) – Conrad Frix May 18 '12 at 16:41
+1 for Yoda Condition & Pokemon Exception Handling. Never heard those terms before. – John Dibling May 18 '12 at 16:48
@ConradFrix: Not only did they lock it, it has been deleted and now only 10k+ users can see it. – John Dibling May 18 '12 at 16:59
@JohnDibling that was kinda my point I wouldn't mind see that question revived via an [historical lock](http://meta.stackexchange.com/q/126587/148672) – Conrad Frix May 18 '12 at 17:15
Indeed, it's a prime candidate for historical lock. Deleting it was inappropriate and accomplished nothing of value. – R.. GitHub STOP HELPING ICE May 18 '12 at 23:54
"Some developers" == "Amateurs" :) – Super-intelligent Shade Aug 20 '17 at 18:37

score 7 · Answer 2 · answered May 18 '12 at 16:34

7

The second version is supposed to be safer.

In case you forget one equal sign, it does not change the value of i to zero.

answered May 18 '12 at 16:34

Benoît

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score 5 · Answer 3 · answered May 18 '12 at 16:35

5

Functionally, they are the same in C; I'm not sure about other languages where ugly things like operator overloading come into play.

Stylistically, the latter is extremely counter-intuitive and personally I find it extremely ugly. The point is to get the compiler to throw an error when you accidentally write = instead of ==, but good compilers have an option to warn you about this anyway so it's unnecessary.

answered May 18 '12 at 16:35

R.. GitHub STOP HELPING ICE

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Operator overloading is beautiful! (When applied correctly.) That's one of the things I love about C++, again and again. – leemes May 29 '12 at 00:19

score 3 · Answer 4 · answered May 18 '12 at 16:49

For C++, it's possible, though unlikely, that there could be a difference. It depends upon what i's type is. e.g.

struct Foo
{
    int x;
};

bool operator==(Foo lhs, int rhs)
{
    return lhs.x == rhs;
}

bool operator==(int lhs, Foo rhs)
{
    std::cout << "Hi!";
    return true;
}

Someone who writes code like that should of course be shot.

score 2 · Answer 5 · edited May 23 '17 at 12:22

2

Yep they are same as far as C# is concerned. For more complex situations visit A==B vs B==A, What are the differences

edited May 23 '17 at 12:22

Community

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answered May 18 '12 at 16:35

Lav

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score 1 · Answer 6 · answered May 18 '12 at 16:34

1

When you write (0==i) the error of using single equal to sign by mistake (e.g. ) if ( i = 0) is eliminated. Nothing else.

answered May 18 '12 at 16:34

vrk001

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score 1 · Answer 7 · answered May 18 '12 at 16:34

1

no difference, some people prefer the second one to catch the common mistake of doing assignment (=) instead of equality test (==)

0 = i would fail at compilation

answered May 18 '12 at 16:34

Pierre Lacave

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score 0 · Answer 8 · answered May 18 '12 at 16:34

In C# there is no difference. However in C++ there was a difference in performance which is why you see both used in C# code these days - actually I'm thinking of i++ vs ++i about performance - 0 == i is a common coding recommendation in C/C++ to avoid i = 0 as an accidental operation

Is there a difference between i==0 and 0==i?

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