Best Practice on IF/ELSE Statement Order

Question

Which is a better practice? (I\'m coding in .Net if that makes a difference)

IF condition = true THEN
   ...true action--even if rare...
ELSE
   ...action
E         


        

Answer 1

Use whichever makes the code easier to read. This is usually the second of your options.

Edit

In a lot of cases, it depends on what you're trying to achieve, for example, if you want to check that a connection started correctly:

Connect()
if connected then
    SendString("Hello!")
else
    FlagConnectionFailed()
endif

Whereas if you want to catch an error:

' Just about to send something
if not connected then
    FlagConnectionLost()
    return
endif
SendString("Still connected!")

But you may even want to:

Disconnect()
if not connected then
    return "Complete"
else
    FlagConnectionDisconnectFailure()
endif

(I'm not a VB programmer, so the syntax above is largely made up!)

Answer 2

Go with the most readable version for your specific case, and by the way, don't compare a boolean expression to true and false. Use condition and Not condition (!condition in C#.)

if (condition == true) // bad
if (condition) // better 

Answer 3

In the final assembly/machine code, it does make a difference. The statement which is most likely to be executed is done in the path without the branch. This way, the pipeline isn't broken causing valuable cycles to be lost.

I have no clue if the compiler leaves your if then statement order intact and this way forces the assembly to take this optimized route.

I have read that visual studio 2008 (when it was announced) would have an optimization functionality where the compiler adds measurements at branches and then during runtime measures how often a certian path is taken. Then in subsequent recompiles the most optimal code path is preferred.

I have no clue if this feature ever made it past the 'design/academic phase'

Answer 4

First of all, you shouldn't compare to boolean values, this is, do

if condition then

instead of

if condition = true then

About your question, it depends on the natural variable names, IMO.

For example, if you are creating a client that needs to check if it's connected (the most common case)

if connected then
    //Proceed
else
    //Throw error
end if

Or, if you are creating a different program, where you have a variable, say, retrieved and you want to know if the content has been retrieved

if not retrieved then
   //Error
end if

Do not do

if retrieved then
else
    //Error
end if