What is the difference between And and AndAlso in VB NET

Question

In VB NET  what is the difference between And and AndAlso  Which should I use

User · Accepted Answer

The And operator evaluates both sides  where AndAlso evaluates the right side if and only if the left side is true   An example   If mystring IsNot Nothing And mystring Contains  Foo   Then     bla bla End If   The above throws an exception if mystring   Nothing  If mystring IsNot Nothing AndAlso mystring Contains  Foo   Then     bla bla End If   This one does not throw an exception   So if you come from the C  world  you should use AndAlso like you would use  amp  amp    More info here  http   www panopticoncentral net 2003 08 18 the-ballad-of-andalso-and-orelse

User · Answer

AndAlso is much like And  except it works like  amp  amp  in C   C    etc   The difference is that if the first clause  the one before AndAlso  is true  the second clause is never evaluated - the compound logical expression is  short circuited    This is sometimes very useful  e g  in an expression such as   If Not IsNull myObj  AndAlso myObj SomeProperty   3 Then        End If   Using the old And in the above expression would throw a NullReferenceException if myObj were null

User · Answer

If Bool1 And Bool2 Then   Evaluates both Bool1 and Bool2  If Bool1 AndAlso Bool2 Then   Evaluates Bool2 if and only if Bool1 is true

User · Answer

A simple way to think about it is using even plainer English  If Bool1 And Bool2 Then If  both are true  Then   If Bool1 AndAlso Bool2 Then If  first is true then evaluate the second  Then

User · Answer

For majority of us OrElse and AndAlso will do the trick except for a few confusing exceptions  less than 1  where we may have to use Or and And    Try not to get carried away by people showing off their boolean logics and making it look like a rocket science    It s quite simple and straight forward and occasionally your system may not work as expected because it doesn t like your logic in the first place  And yet your brain keeps telling you that his logic is 100  tested and proven and it should work  At that very moment stop trusting your brain and ask him to think again or  not OrElse or maybe OrElse  you force yourself to look for another job that doesn t require much logic

User · Answer

Just for all those people who say side effects are evil  a place where having two side effects in one condition is good would be reading two file objects in tandem   While File1 Seek Next Row   And File2 Seek Next Row       Str1   File1 GetRow       Str2   File2 GetRow   End While   Using the And ensures that a row is consumed every time the condition is checked  Whereas AndAlso might read the last line of File1 and leave File2 without a consumed line   Of course the code above wouldn t work  but I use side effects like this all the time and wouldn t consider it  bad  or  evil  code as some would lead you to believe  It s easy to read and efficient

User · Answer

To understand with words not cods  Use Case With    And    the compiler will check all conditions so if you are checking that an object could be    Nothing    and then you are checking one  of it   s properties you will have a run time error  But with AndAlso with the first    false    in the conditions it will checking the next one so you will not have an error

User · Answer

Also see Stack Overflow question  Should I always use the AndAlso and OrElse operators    Also  A comment for those who mentioned using And if the right side of the expression has a side-effect you need   If the right side has a side effect you need  just move it to the left side rather than using  And   You only really need  And  if both sides have side effects  And if you have that many side effects going on you re probably doing something else wrong  In general  you really should prefer AndAlso

User · Answer

If Bool1 And Bool2 Then   Evaluates both Bool1 and Bool2  If Bool1 AndAlso Bool2 Then   Evaluates Bool2 if and only if Bool1 is true

User · Answer

Also see Stack Overflow question  Should I always use the AndAlso and OrElse operators    Also  A comment for those who mentioned using And if the right side of the expression has a side-effect you need   If the right side has a side effect you need  just move it to the left side rather than using  And   You only really need  And  if both sides have side effects  And if you have that many side effects going on you re probably doing something else wrong  In general  you really should prefer AndAlso

User · Answer

In addition to the answers above  AndAlso provides a conditioning process known as short circuiting  Many programming languages have this functionality built in like vb net does  and can provide substantial performance increases in long condition statements by cutting out evaluations that are unneccessary   Another similar condition is the OrElse condition which would only check the right condition if the left condition is false  thus cutting out unneccessary condition checks after a true condition is found   I would advise you to always use short circuiting processes and structure your conditional statements in ways that can benefit the most by this  For example  test your most efficient and fastest conditions first so that you only run your long conditions when you absolutely have to and short circuit the other times

User · Answer

For majority of us OrElse and AndAlso will do the trick except for a few confusing exceptions  less than 1  where we may have to use Or and And    Try not to get carried away by people showing off their boolean logics and making it look like a rocket science    It s quite simple and straight forward and occasionally your system may not work as expected because it doesn t like your logic in the first place  And yet your brain keeps telling you that his logic is 100  tested and proven and it should work  At that very moment stop trusting your brain and ask him to think again or  not OrElse or maybe OrElse  you force yourself to look for another job that doesn t require much logic

User · Answer

The And operator will check all conditions in the statement before continuing  whereas the Andalso operator will stop if it knows the condition is false  For example   if x   5 And y   7   Checks if x is equal to 5  and if y is equal to 7  then continues if both are true   if x   5 AndAlso y   7   Checks if x is equal to 5  If it s not  it doesn t check if y is 7  because it knows that the condition is false already   This is called short-circuiting    Generally people use the short-circuiting method if there s a reason to explicitly not check the second part if the first part is not true  such as if it would throw an exception if checked  For example   If Not Object Is Nothing AndAlso Object Load     If that used And instead of AndAlso  it would still try to Object Load   even if it were nothing  which would throw an exception

User · Answer

The And operator will check all conditions in the statement before continuing  whereas the Andalso operator will stop if it knows the condition is false  For example   if x   5 And y   7   Checks if x is equal to 5  and if y is equal to 7  then continues if both are true   if x   5 AndAlso y   7   Checks if x is equal to 5  If it s not  it doesn t check if y is 7  because it knows that the condition is false already   This is called short-circuiting    Generally people use the short-circuiting method if there s a reason to explicitly not check the second part if the first part is not true  such as if it would throw an exception if checked  For example   If Not Object Is Nothing AndAlso Object Load     If that used And instead of AndAlso  it would still try to Object Load   even if it were nothing  which would throw an exception

User · Answer

Just for all those people who say side effects are evil  a place where having two side effects in one condition is good would be reading two file objects in tandem   While File1 Seek Next Row   And File2 Seek Next Row       Str1   File1 GetRow       Str2   File2 GetRow   End While   Using the And ensures that a row is consumed every time the condition is checked  Whereas AndAlso might read the last line of File1 and leave File2 without a consumed line   Of course the code above wouldn t work  but I use side effects like this all the time and wouldn t consider it  bad  or  evil  code as some would lead you to believe  It s easy to read and efficient

User · Answer

In addition to the answers above  AndAlso provides a conditioning process known as short circuiting  Many programming languages have this functionality built in like vb net does  and can provide substantial performance increases in long condition statements by cutting out evaluations that are unneccessary   Another similar condition is the OrElse condition which would only check the right condition if the left condition is false  thus cutting out unneccessary condition checks after a true condition is found   I would advise you to always use short circuiting processes and structure your conditional statements in ways that can benefit the most by this  For example  test your most efficient and fastest conditions first so that you only run your long conditions when you absolutely have to and short circuit the other times

User · Answer

To understand with words not cods  Use Case With    And    the compiler will check all conditions so if you are checking that an object could be    Nothing    and then you are checking one  of it   s properties you will have a run time error  But with AndAlso with the first    false    in the conditions it will checking the next one so you will not have an error

User · Answer

Also see Stack Overflow question  Should I always use the AndAlso and OrElse operators    Also  A comment for those who mentioned using And if the right side of the expression has a side-effect you need   If the right side has a side effect you need  just move it to the left side rather than using  And   You only really need  And  if both sides have side effects  And if you have that many side effects going on you re probably doing something else wrong  In general  you really should prefer AndAlso

User · Answer

The And operator will check all conditions in the statement before continuing  whereas the Andalso operator will stop if it knows the condition is false  For example   if x   5 And y   7   Checks if x is equal to 5  and if y is equal to 7  then continues if both are true   if x   5 AndAlso y   7   Checks if x is equal to 5  If it s not  it doesn t check if y is 7  because it knows that the condition is false already   This is called short-circuiting    Generally people use the short-circuiting method if there s a reason to explicitly not check the second part if the first part is not true  such as if it would throw an exception if checked  For example   If Not Object Is Nothing AndAlso Object Load     If that used And instead of AndAlso  it would still try to Object Load   even if it were nothing  which would throw an exception

User · Answer

AndAlso is much like And  except it works like  amp  amp  in C   C    etc   The difference is that if the first clause  the one before AndAlso  is true  the second clause is never evaluated - the compound logical expression is  short circuited    This is sometimes very useful  e g  in an expression such as   If Not IsNull myObj  AndAlso myObj SomeProperty   3 Then        End If   Using the old And in the above expression would throw a NullReferenceException if myObj were null

User · Answer

AndAlso is much like And  except it works like  amp  amp  in C   C    etc   The difference is that if the first clause  the one before AndAlso  is true  the second clause is never evaluated - the compound logical expression is  short circuited    This is sometimes very useful  e g  in an expression such as   If Not IsNull myObj  AndAlso myObj SomeProperty   3 Then        End If   Using the old And in the above expression would throw a NullReferenceException if myObj were null

User · Answer

Interestingly none of the answers mentioned that And and Or in VB NET are bit operators whereas OrElse and AndAlso are strictly Boolean operators   Dim a   3 OR 5   Will set a to the value 7  011 or 101   111 Dim a   3 And 5   Will set a to the value 1  011 and 101   001 Dim b   3 OrElse 5   Will set b to the value true and not evaluate the 5 Dim b   3 AndAlso 5   Will set b to the value true after evaluating the 5 Dim c   0 AndAlso 5   Will set c to the value false and not evaluate the 5   Note  a non zero integer is considered true  Dim e   not 0 will set e to -1 demonstrating Not is also a bit operator      and  amp  amp   the C  versions of OrElse and AndAlso  return the last evaluated expression which would be 3 and 5 respectively  This lets you use the idiom v    5 in C  to give 5 as the value of the expression when v is null or  0 and an integer  and the value of v otherwise  The difference in semantics can catch a C  programmer dabbling in VB NET off guard as this  default value idiom  doesn t work in VB NET   So  to answer the question  Use Or and And for bit operations  integer or Boolean   Use OrElse and AndAlso to  short circuit  an operation to save time  or test the validity of an evaluation prior to evaluating it  If valid evaluation  andalso evaluation then or if not  unsafe evaluation  orelse  not evaluation   then  Bonus  What is the value of the following   Dim e   Not 0 And 3

User · Answer

Interestingly none of the answers mentioned that And and Or in VB NET are bit operators whereas OrElse and AndAlso are strictly Boolean operators   Dim a   3 OR 5   Will set a to the value 7  011 or 101   111 Dim a   3 And 5   Will set a to the value 1  011 and 101   001 Dim b   3 OrElse 5   Will set b to the value true and not evaluate the 5 Dim b   3 AndAlso 5   Will set b to the value true after evaluating the 5 Dim c   0 AndAlso 5   Will set c to the value false and not evaluate the 5   Note  a non zero integer is considered true  Dim e   not 0 will set e to -1 demonstrating Not is also a bit operator      and  amp  amp   the C  versions of OrElse and AndAlso  return the last evaluated expression which would be 3 and 5 respectively  This lets you use the idiom v    5 in C  to give 5 as the value of the expression when v is null or  0 and an integer  and the value of v otherwise  The difference in semantics can catch a C  programmer dabbling in VB NET off guard as this  default value idiom  doesn t work in VB NET   So  to answer the question  Use Or and And for bit operations  integer or Boolean   Use OrElse and AndAlso to  short circuit  an operation to save time  or test the validity of an evaluation prior to evaluating it  If valid evaluation  andalso evaluation then or if not  unsafe evaluation  orelse  not evaluation   then  Bonus  What is the value of the following   Dim e   Not 0 And 3

User · Answer

AndAlso is much like And  except it works like  amp  amp  in C   C    etc   The difference is that if the first clause  the one before AndAlso  is true  the second clause is never evaluated - the compound logical expression is  short circuited    This is sometimes very useful  e g  in an expression such as   If Not IsNull myObj  AndAlso myObj SomeProperty   3 Then        End If   Using the old And in the above expression would throw a NullReferenceException if myObj were null

User · Answer

If Bool1 And Bool2 Then   Evaluates both Bool1 and Bool2  If Bool1 AndAlso Bool2 Then   Evaluates Bool2 if and only if Bool1 is true

User · Answer

Also see Stack Overflow question  Should I always use the AndAlso and OrElse operators    Also  A comment for those who mentioned using And if the right side of the expression has a side-effect you need   If the right side has a side effect you need  just move it to the left side rather than using  And   You only really need  And  if both sides have side effects  And if you have that many side effects going on you re probably doing something else wrong  In general  you really should prefer AndAlso

User · Answer

The And operator will check all conditions in the statement before continuing  whereas the Andalso operator will stop if it knows the condition is false  For example   if x   5 And y   7   Checks if x is equal to 5  and if y is equal to 7  then continues if both are true   if x   5 AndAlso y   7   Checks if x is equal to 5  If it s not  it doesn t check if y is 7  because it knows that the condition is false already   This is called short-circuiting    Generally people use the short-circuiting method if there s a reason to explicitly not check the second part if the first part is not true  such as if it would throw an exception if checked  For example   If Not Object Is Nothing AndAlso Object Load     If that used And instead of AndAlso  it would still try to Object Load   even if it were nothing  which would throw an exception

User · Answer

If Bool1 And Bool2 Then   Evaluates both Bool1 and Bool2  If Bool1 AndAlso Bool2 Then   Evaluates Bool2 if and only if Bool1 is true

User · Answer

A simple way to think about it is using even plainer English  If Bool1 And Bool2 Then If  both are true  Then   If Bool1 AndAlso Bool2 Then If  first is true then evaluate the second  Then

[vb.net] What is the difference between And and AndAlso in VB.NET?

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