Difference Between = and ==

TurnipTruck

Greetings,

I am examining some code. What is the difference between = and ==

Thanks.

ekeppel

It is a relational operator that can be substituted with a single = in most cases. You can look up relational operators in NS help to see some info on it.

Correct me if I'm wrong but this is how I've always viewed it:

= is for assignment generally, but can be used in a relational expression also

For example, either of the following lines should work fine:
intMyInt = 1
IF(intMyInt = 1) DoFunction()

== is relational only (boolean expressions)

For example:
IF(intMyInt == 1) DoFunction()


I don't really use the == but it can make the code look better and it is easier to pick out relational expressions since it goes right along with && (AND), || (OR), etc.

--Eric

Chip Moody

= can serve two functions, assignment and comparison - I.E.:

X = 3 <-- assign the value of 3 to the variable called X
IF (X = 3) <-- comparison - is one value equal to another?

== is found in more common programming languages, and to the best of my knowledge is simply a "comparison only" function.

IF (X == 3) <-- same as above
X == 3 <-- not an assignment operator, so this will fail to compile

In C, = does assignment only, and using it the way we're used to in Netlinx/Axcess for comparison will cause problems...

- Chip

P.S. Of course, some days I feel nostalgic and miss Pascal syntax, where := is the assignment operator.

usefletch

Chip is correct. Netlinx compiler allows both terms. The only place it seems required is in ambiguous code. Where the compiler can not differentiate assignment or comparison.
As a C/C++ programmer, the netlinx compiler allows my normal usage of both to compile just fine.

Joe Hebert

I agree with all assessments, however, I believe the correct answer to the original question is...one equal sign. Ok, stupid joke.

This is a tad off topic but you can also drop the = sign(s) for comparison and do something like:

IF(x) //will drop thru if x is anything other than 0.

I don?t know if others consider that proper coding or not.

jjames

Joe Hebert wrote:

I agree with all assessments, however, I believe the correct answer to the original question is...one equal sign. Ok, stupid joke.

This is a tad off topic but you can also drop the = sign(s) for comparison and do something like:

IF(x) //will drop thru if x is anything other than 0.

I don’t know if others consider that proper coding or not.

I use that all the time. And I will also do:

IF(!x)
{
  // Do stuff if it is zero
}

Though, when comparing multiple things that need to be zero in order for the IF statement to be true, I typically spell it out like so....

IF(x==FALSE && y==TRUE && z==FALSE)

Rather than saying:

IF((!x) && (y) && (!z))

Though both are identical IF statements. The use of the added parenthesis is helpful / recommended when doing something like the second example.

Also, == NetLinx gives a compiler error when it is used for assignment (for the obvious reasons.)

NMarkRoberts

I take this very literal coding rule a step further when dealing with muting, which can be confusing as it is reversed sense (muting on means sound off)

Muted = 1
Unmuted = 0

if (bMicMuted = Muted) etc

DHawthorne

I always use == for comparisons, even though a single = may work. It's partly from my C++ background, where using an = for comparisons assigns at the same time, but mostly it's so there can be no possible doubt in case I missed a situation the compiler finds ambiguous.

And yes, If(x) is a a perfectly valid statement - I use that kind of syntax all the time; any non-zero evaluation for x returns as true.