What is the difference between the | and || or operators?

Just like the & and && operator, the double Operator is a "short-circuit" operator.

For example:

if(condition1 || condition2 || condition3)

If condition1 is true, condition 2 and 3 will NOT be checked.

if(condition1 | condition2 | condition3)

This will check conditions 2 and 3, even if 1 is already true. As your conditions can be quite expensive functions, you can get a good performance boost by using them.

There is one big caveat, NullReferences or similar problems. For example:

if(class != null && class.someVar < 20)

If class is null, the if-statement will stop after class != null is false. If you only use &, it will try to check class.someVar and you get a nice NullReferenceException. With the Or-Operator that may not be that much of a trap as it's unlikely that you trigger something bad, but it's something to keep in mind.

No one ever uses the single & or | operators though, unless you have a design where each condition is a function that HAS to be executed. Sounds like a design smell, but sometimes (rarely) it's a clean way to do stuff. The & operator does "run these 3 functions, and if one of them returns false, execute the else block", while the | does "only run the else block if none return false" - can be useful, but as said, often it's a design smell.

There is a Second use of the | and & operator though: Bitwise Operations.

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|| is the logical OR operator. It sounds like you basically know what that is. It's used in conditional statements such as if, while, etc.

condition1 || condition2

Evaluates to true if either condition1 OR condition2 is true.

| is the bitwise OR operator. It's used to operate on two numbers. You look at each bit of each number individually and, if one of the bits is 1 in at least one of the numbers, then the resulting bit will be 1 also. Here are a few examples:

A = 01010101
B = 10101010
A | B = 11111111

A = 00000001
B = 00010000
A | B = 00010001

A = 10001011
B = 00101100

A | B = 10101111

Hopefully that makes sense.

So to answer the last two questions, I wouldn't say there are any caveats besides "know the difference between the two operators." They're not interchangeable because they do two completely different things.

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One is a "bitwise or".

10011b | 01000b => 11011b

The other is a logic or.

true or false => true

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Good question. These two operators work the same in PHP and C#.

| is a bitwise OR. It will compare two values by their bits. E.g. 1101 | 0010 = 1111. This is extremely useful when using bit options. E.g. Read = 01 (0X01) Write = 10 (0X02) Read-Write = 11 (0X03). One useful example would be opening files. A simple example would be:

File.Open(FileAccess.Read | FileAccess.Write);  //Gives read/write access to the file

|| is a logical OR. This is the way most people think of OR and compares two values based on their truth. E.g. I am going to the store or I will go to the mall. This is the one used most often in code. For example:

if(Name == "Admin" || Name == "Developer") { //allow access } //checks if name equals Admin OR Name equals Developer

PHP Resource: http://us3.php.net/language.operators.bitwise

C# Resources: http://msdn.microsoft.com/en-us/library/kxszd0kx(VS.71).aspx

http://msdn.microsoft.com/en-us/library/6373h346(VS.71).aspx

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& - (Condition 1 & Condition 2): checks both cases even if first one is false

&& - (Condition 1 && Condition 2): dosen't bother to check second case if case one is false

&& - operator will make your code run faster, professionally & is rarely used

| - (Condition 1 | Condition 2): checks both cases even if case 1 is true

|| - (Condition 1 || Condition 2): dosen't bother to check second case if first one is true

|| - operator will make your code run faster, professionally | is rarely used

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Simple example in java

public class Driver {

  static int x;
  static int y;

public static void main(String[] args) 
throws Exception {

System.out.println("using double pipe");
    if(setX() || setY())
        {System.out.println("x = "+x);
        System.out.println("y = "+y);
        }



System.out.println("using single pipe");
if(setX() | setY())
    {System.out.println("x = "+x);
    System.out.println("y = "+y);
    }

}

 static boolean setX(){
      x=5;
     return true;
  }
 static boolean setY(){
      y=5;
      return true;
  }
}

output :

using double pipe
x = 5
y = 0
using single pipe
x = 5
y = 5

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By their mathematical definition, OR and AND are binary operators; they verify the LHS and RHS conditions regardless, similarly to | and &.

|| and && alter the properties of the OR and AND operators by stopping them when the LHS condition isn't fulfilled.

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For bitwise | and Logicall ||

OR

bitwise & and logicall &&

it means if( a>b | a==0) in this first left a>b will be evaluated and then a==0 will be evaluated then | operation will be done

but in|| if a>b then if wont check for next RHS

Similarly for & and &&

if(A>0 & B>0)

it will evalue LHS and then RHS then do bitwise & but

in(A>0 && B>0)

if(A>0) is false(LHS) it will directly return false;

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The single pipe, |, is one of the bitwise operators.

From Wikipedia:

In the C programming language family, the bitwise OR operator is "|" (pipe). Again, this operator must not be confused with its Boolean "logical or" counterpart, which treats its operands as Boolean values, and is written "||" (two pipes).

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The | operator performs a bitwise OR of its two operands (meaning both sides must evaluate to false for it to return false) while the || operator will only evaluate the second operator if it needs to.

http://msdn.microsoft.com/en-us/library/kxszd0kx(VS.71).aspx

http://msdn.microsoft.com/en-us/library/6373h346(VS.71).aspx

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The singe pipe "|" is the "bitwise" or and should only be used when you know what you're doing. The double pipe "||" is a logical or, and can be used in logical statements, like "x == 0 || x == 1".

Here's an example of what the bitwise or does: if a=0101 and b=0011, then a|b=0111. If you're dealing with a logic system that treats any non-zero as true, then the bitwise or will act in the same way as the logical or, but it's counterpart (bitwise and, "&") will NOT. Also the bitwise or does not perform short circuit evaluation.

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A single pipe (|) is the bitwise OR operator.

Two pipes (||) is the logical OR operator.

They are not interchangeable.

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