Short-circuit Evaluation in C#


Hi everyone , in this article we’ll discuss C# short-circuit logical operators && and || in depth. Most of us must have used these operators before, but many of them don’t know about why we use && instead of &.Use of these operators(&& and ||) is one of the best practice over non short-circuit operators & and |. So you should know how it works, where to use them and how they increase speed of execution. let’s get started.

NOTE : all of the code snippet given in this  are well tested.

What is Short-Circuit in C#?

Short-circuit is a tricky method for evaluating logical operators AND and OR. In this method, whole expression can be evaluated to true or false without evaluating all sub expressions.

Consider  following c# code snippet using & and |

While debugging it looks like below

short circuit in c#

In the above program both operands Condition1() and Condition2() are evaluated.

“For AND operations if any of the operand evaluated to false then total expression evaluated to false then there is no need to evaluate remaining expressions, And in case of OR operation if any of the operand evaluated to true then remaining evaluations can be skipped.”

This type of skipping is done through short-circuited evaluation.For that, in the above program, & is replaced with  && and | is replaced with ||, then debugging will be like this

&& and || in c#You can see the skipping of evaluations due to short-circuit evaluation. Consider following example

in the above if clause, Condition1() will not be evaluated because whatever be the value of Condition1() whole expression will be false.If we use & instead of &&, it will execute Condition1() alsoSo always try to stick with short-circuited version, There is one little point you should aware of, that is  Side effect.I will tell you what it means in later parts of this article.

&& Vs & or || Vs |

First difference between them is short-circuit evaluation. Before getting into remaining differences let’s grab some basics that might be helpful to understand the rest.

AND, OR operators can be found in the following ways :-

& ( single ampersand ) – Logical AND operator
| ( single pipeline) – Logical OR operator
Both of these operators are non short-circuit in nature.

&& ( double ampersand ) – Conditional AND operator
|| ( double pipeline) – Conditional OR operator
Both of these are short-circuited operators and collectively knows as Conditional Logical Operators.

Order of Evaluation

Order of execution  of any of these operators are from left to right.
In the following lines of code

Expression1 will be evaluated first then Expression2 and so on.

Remaining Differences

& and | can be used as  both Boolean operand as well as Numeric operands like Bit-wise operation But && and || operands can only be applied to Boolean operands.

-& operator can be used as either unary or binary operator. that is, unary & can be used to get address of it’s operand in unsafe context.

Examples :

as Binary Operator

– Bit wise Operation

-Logical Operation

as Unary Operator

& can be used as addressof-expression in unsafe mode.for more detais follow this link from msdn

How to Use && in C#

In this section I will tell you how to use && with the help of some practical examples.In the same way you can understand how you can make use of || operator.

1.Prevent Exceptions

If you asked to write a c# program for checking 5th  element in a given array is odd or not.It is better to implement following if clause.

If the && were replaced with &.it will cause Index was outside the bounds of the array exception when array does not contains 5 elements.

2.Ordering Expressions to Reduce Performance Impact
Like we said, order of evaluation is from left to right.So if you have a series of operands for && operator as below and each of them are independent on other expression.

It is better to arrange them in the order of their complexity.For example, if you are dealing with a project including lot of data base interactions, move all those DB methods to right side of if clause so that in many of the instances these methods won’t be executed if preceding operands were false.

Side Effect

Consider the following example

As a result of short circuiting second operand in second if clause will not execute, so value of i remains same as before.this effect is called Side effect, I would say it is a Right Side effect right? 😉

So when you use them, you should be  aware of this effect and these effects are practically seen in rare situations.


Short circuited logical operators in C# are && and ||, They are efficient and fast version of logical operators in C#.So it is a good practice to use them and there is no reason no to use them.
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  • Thank you! This article is really great!

    Chek Wei Tan 2 weeks ago Reply

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