Conditional Statements difference

Question

Is there any difference between below two statements

if (null != obj)

and

if (obj != null)

If both treate

Answer 1

They are exactly the same.

Some people prefer to put the null as the first part of the expression to avoid errors like this

if (obj = null)  // should be obj == null

But of course this doesn't apply to the != operator, so in your example it's just a difference of style.

Answer 2

The use of the first form

if (blah == obj) 

stems from the days when compilers would not catch if (obj = blah) i.e. unintentional assignment, unless compile warning level was set to maximum

Answer 3

The first is a Yoda condition. Use it you should not.

Answer 4

No, there is not. It's exactly the same.

The style null == obj is sometimes just used to prevent the common typo obj = null to not accidently assign null to a variable, but with != there's absolutely no reason to do so.

In .NET it won't actually compile for the typo obj = null.
So the compiler prevents you from accidently doing it.

The Yoda condition comes originally from other languages, where this compiler feature is missing.

Answer 5

First type of statement came from C/C++, where was possible to pass not boolean values to condition verification. E.g. anything not 0 was true, and zero was false:

if (5) { } // true
if (0) { } // false

Sometimes it created problems if you forgot to type one '=' char:

if (x = 5) { }   // this was true always and changed x value
if (x == 5) { }  // this was true, if x was equal to 5

So, Yoda syntax was used, to receive compiler error in case one '=' was missed:

if (5 = x) { }   // this was generating compiler error for absent-minded programmers
if (5 == x) { }  // this was true, if x was equal to 5

C# allow only boolean value in conditions, So

if (x = 5) { }   // this won't compile
if (x == 5) { }  // this is true, if x was equal to 5

What about boolean types?

if (y = true) { }
if (y == true) { }

Well, this is useless code, because you can just write if (y). Conclusion: Yoda syntax is gone with C/C++ and you do not need to use it anymore.

Answer 6

No, but the second way is more common and more readable (and more logical in my opinion)