CODEWITHSUNDEEP
c#boolean-expression
GuidoG
GuidoG

Reputation: 12014

In what order are boolean expressions evaluated

I have been looking for an explanation for the order in which boolean expressions are evaluated but cannot find one.

Take a look at this statement :

if (locClsTanken.PlaceID == -1 && locRwF.PlaceID > -1 || locClsTanken.DagPrijs == 0)

How is this evaluated.
will it be like this : 

if ((locClsTanken.PlaceID == -1 && locRwF.PlaceID > -1) || locClsTanken.DagPrijs == 0)

or like this :

if (locClsTanken.PlaceID == -1 && (locRwF.PlaceID > -1 || locClsTanken.DagPrijs == 0))

Is there some documentation about this I dont know the correct search term because english is not my language.

I know I can test it but I would like to find the documentation about this so I can fully understand it

Upvotes: 1

Views: 1873

Answers (3)

Bathsheba
Bathsheba

Reputation: 234715

&& has higher precedence than ||, so

locClsTanken.PlaceID == -1 && locRwF.PlaceID > -1 || locClsTanken.DagPrijs == 0

is evaluated as

(locClsTanken.PlaceID == -1 && locRwF.PlaceID > -1) || locClsTanken.DagPrijs == 0

Note that && and || are also short-circuited so evaluation of the right-hand operand only occurs if that could change the result following the evaluation of the left-hand one.

Reference: https://msdn.microsoft.com/en-gb/library/aa691323(v=vs.71).aspx

Upvotes: 5

RononDex
RononDex

Reputation: 4183

In C# the compiler moves from left to right, meaning it will evaluate the left most expression first (in your case that is locClsTanken.PlaceID == -1)

Also, && has higher priority than || --> gets evaluated first

However, what might confuse you is how the compiler handels the && and ||. There is a difference between & and &&.

& means both expressions have to be true and both expressions are evaluated. However, && only causes one expression to be evaluated first. If the first expression fails, then the second one isn't even evaluated, because in order for && to be true both expressions need to be true. If the first one already fails && is always false --> && is faster than & and more "inteligent"

Upvotes: 2

Hicham Bouchikhi
Hicham Bouchikhi

Reputation: 726

The expression are readed from left to right in addition to that the && has higher precedence than ||.
So in your case it's would be like 

if ((locClsTanken.PlaceID == -1 && locRwF.PlaceID > -1) || locClsTanken.DagPrijs == 0)

And the technical therm that you're looking for is Operators Precedence take a look to this link:Operators Precedence

Upvotes: 2

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