What is the difference between the and or operators

Question

I have always used     two pipes  in OR expressions  both in C  and PHP  Occasionally I see a single pipe used     What is the difference between those two usages  Are there any caveats when using one over the other or are they interchangeable

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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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amp  -  Condition 1  amp  Condition 2   checks both cases even if first one is false   amp  amp  -  Condition 1  amp  amp  Condition 2   dosen t bother to check second case if case one                                     is false    amp  amp  - operator will make your code run faster  professionally  amp  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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Just like the  amp  and  amp  amp  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  amp  amp  class someVar  lt  20    If class is null  the if-statement will stop after class    null is false  If you only use  amp   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  amp  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  amp  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  amp  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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By their mathematical definition  OR and AND are binary operators  they verify the LHS and RHS conditions regardless  similarly to   and  amp        and  amp  amp  alter the properties of the OR and AND operators by stopping them when the LHS condition isn t fulfilled

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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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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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One is a  bitwise or       10011b   01000b    11011b   The other is a logic or      true or false    true

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For bitwise   and Logicall    OR bitwise  amp  and logicall  amp  amp  it means   if  a gt b   a  0  in this first left a gt b will be evaluated and then a  0 will be evaluated then   operation will be done but in   if a gt b then if wont check for next RHS Similarly for  amp  and  amp  amp  if A gt 0  amp  B gt 0  it will evalue LHS and then RHS then do bitwise  amp  but in A gt 0  amp  amp  B gt 0  if A gt 0  is false LHS  it will directly return false

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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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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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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    amp    will NOT  Also the bitwise or does not perform short circuit evaluation

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