AndAlso

[Matt]

Hi, I am new to vb.net. In using the If condition, can we
use either of And or AndAlso. Whats the difference ? In VB
I have always used And.
For eg.
if num > 10 AndAlso num < 20

Thanks.
Matt

[Phill. W]

"Matt" <an*******@disc ussions.microso ft.com> wrote in message
news:01******** *************** *****@phx.gbl.. .

Hi, I am new to vb.net. In using the If condition, can we
use either of And or AndAlso. Whats the difference ?

The "AndAlso" operator uses "short-circuit" evaluation - if the
First condition is False, the second isn't even evaluated. Useful
for things like this:

dataSet = FunctionThatRet urnsADataSet_Or Nothing()

' Did I get a DataSet with just one row in it?
If Not ( dataSet Is Nothing ) _
AndAlso dataSet.Tables( 0 ).Rows = 1 _
Then

"And" always works out /both/ expressions.

HTH,
Phill W.

[One Handed Man [ OHM# ]]

*And* evaluates both Expression1 and Expression2. Whereas, *AndAlso*,
provides a means to perform short-circuiting the evaluation process is some
cases.

False AndAlso True will only evaluate the 'False' and knows it does not
need to evaluate the 'True' because it already has its answer. This can help
performance if used in a loop.
Regards - OHM


Matt wrote:

Hi, I am new to vb.net. In using the If condition, can we
use either of And or AndAlso. Whats the difference ? In VB
I have always used And.
For eg.
if num > 10 AndAlso num < 20

Thanks.
Matt

--
Best Regards - OHM

O_H_M{at}BTInte rnet{dot}com

[Codemonkey]

In addition to the comments mentioned, there is also an "orelse" operator
which does lazy evaluation using the or operator
e.g.

If True orelse MyReallySlowFun ction() Then
MyReallySlowFun ction() will never get called because "orelse" has evaluated
True and so does not need to evaluate MyReallySlowFun ction()
HTH,

Trev.

[copyco]

In the case of "if x and y": this is true if both x and y are true.

In the case of "if x andalso y": this is true only if x is true
regardless of the value of y, and if x is true and y is true.

Basically ANDALSO is the same as regular AND except that the first value
you are testing MUST be true to evaluate as true.

Is that confusing enough?
Matt wrote:

Hi, I am new to vb.net. In using the If condition, can we
use either of And or AndAlso. Whats the difference ? In VB
I have always used And.
For eg.
if num > 10 AndAlso num < 20

Thanks.
Matt

[David]

On 2004-01-09, copyco <co****@anon.co m> wrote:

In the case of "if x and y": this is true if both x and y are true.

In the case of "if x andalso y": this is true only if x is true
regardless of the value of y, and if x is true and y is true.
Umm, no. Read the rest of the thread for details, but if x is true
and y is false, ' x andalso y' will evaluate to false.
Basically ANDALSO is the same as regular AND except that the first value
you are testing MUST be true to evaluate as true.
Again, no. (and this definition is different than your first
definition, but both are wrong).
Is that confusing enough?

Yes, which is why it's not done that way.

More specifically, 'x and y' and 'x andalso y' will always evaluate to
the same value for boolean values, either true or false.

Postscript: Actually, I suppose that's only true if evaluation order is
guaranteed with the 'And' operator, and I can't find anything that says
it is. So a minor caveat.

--
David
dfoster at
hotpop dot com

[Jeremy Cowles]

Just a useless trivia note:

The real terms for these operations are short-circuiting logical disjunction
(orelse), and short-circuiting logical conjunction (andalso), which most
people refer to as "short-circuited", or "lazy." In .NET it's used for
logical operators, but the concept is broad and could be applied to any
chain of logic.

It basically means, stop processing as soon as possible. Like playing
basketball best 3 out of 5, you don't need to actually play all five games
unless both teams win twice.

~
Jeremy

"Matt" <an*******@disc ussions.microso ft.com> wrote in message
news:01******** *************** *****@phx.gbl.. .

Hi, I am new to vb.net. In using the If condition, can we
use either of And or AndAlso. Whats the difference ? In VB
I have always used And.
For eg.
if num > 10 AndAlso num < 20

Thanks.
Matt

[copyco]

David wrote:

On 2004-01-09, copyco <co****@anon.co m> wrote:

In the case of "if x and y": this is true if both x and y are true.

In the case of "if x andalso y": this is true only if x is true
regardless of the value of y, and if x is true and y is true.

Umm, no. Read the rest of the thread for details, but if x is true
and y is false, ' x andalso y' will evaluate to false.

What you just said is what I said, or tried to say. Perhaps you didn't
understand what I wrote, or I didn't word it correctly. So we are in
agreement here.

Basically ANDALSO is the same as regular AND except that the first value
you are testing MUST be true to evaluate as true.

Again, no. (and this definition is different than your first
definition, but both are wrong).

According to the table given in the help file, what I said is correct.
The first value you are testing must be true in order for it to evaluate
to true regarless of the second value. And only when both values are
true does it evaluate to true. See the table below.

If expression1 is / And expression2 is / Value of result is
True True True
True False False
False (not evaluated) False

Is that confusing enough?

Yes, which is why it's not done that way.

More specifically, 'x and y' and 'x andalso y' will always evaluate to
the same value for boolean values, either true or false.

Postscript: Actually, I suppose that's only true if evaluation order is
guaranteed with the 'And' operator, and I can't find anything that says
it is. So a minor caveat.

[David]

On 2004-01-09, copyco <co****@anon.co m> wrote:

David wrote:

On 2004-01-09, copyco <co****@anon.co m> wrote:

In the case of "if x and y": this is true if both x and y are true.

In the case of "if x andalso y": this is true only if x is true
regardless of the value of y, and if x is true and y is true.

Umm, no. Read the rest of the thread for details, but if x is true
and y is false, ' x andalso y' will evaluate to false.

What you just said is what I said, or tried to say. Perhaps you
didn't understand what I wrote, or I didn't word it correctly. So we
are in agreement here.

Perhaps so, but why don't we rephrase your original statement?

In the case of "if x and y": this is true if both x and y are true.

In the case of "if x andalso y": this is true if both x and y are true.
Period. End of discussion as far as the value of the operation goes.

But then what does this phrase fragment mean?

In the case of "if x andalso y": this is true only if x is true
regardless of the value of y...
Basically ANDALSO is the same as regular AND except that the first value
you are testing MUST be true to evaluate as true.

Again, no. (and this definition is different than your first
definition, but both are wrong).

According to the table given in the help file, what I said is correct.

No, the table's not the point here. Both 'And' and 'AndAlso' share
the same table. The problem above is the word "except", since in
both cases the first value MUST be true for the phrase to evaluate
as true. In other words, "the first value you are testing MUST
be true to evaluate as true" is true of both 'And' and 'AndAlso',
so the word "except" makes no sense here.

Now if you really understand this and there's just some grammatical
confusion, then no big deal. But you keep trying to point out
the And/AndAlso difference by saying something about the value
of 'X And Y' vs. 'X AndAlso Y', and that's just not the difference
between the two operators.
The first value you are testing must be true in order for it to
evaluate to true regarless of the second value.
Likewise the second value must be true in order for it to evaluate to
true regardless of the first value.

Those two combined is simply is a very longwinded way of simply
saying...
only when both values are true does it evaluate to true.

And the lines above are true of the 'And' operator as well, so that
hardly points out the difference between them.

--
David
dfoster at
hotpop dot com

[copyco]

You're right. Now go have a cup of hot chocolate.

David wrote:

On 2004-01-09, copyco <co****@anon.co m> wrote:

David wrote:

On 2004-01-09, copyco <co****@anon.co m> wrote:
In the case of "if x and y": this is true if both x and y are true.

In the case of "if x andalso y": this is true only if x is true
regardles s of the value of y, and if x is true and y is true.
Umm, no. Read the rest of the thread for details, but if x is true
and y is false, ' x andalso y' will evaluate to false.

What you just said is what I said, or tried to say. Perhaps you
didn't understand what I wrote, or I didn't word it correctly. So we
are in agreement here.

Perhaps so, but why don't we rephrase your original statement?

In the case of "if x and y": this is true if both x and y are true.

In the case of "if x andalso y": this is true if both x and y are true.
Period. End of discussion as far as the value of the operation goes.

But then what does this phrase fragment mean?

In the case of "if x andalso y": this is true only if x is true
regardles s of the value of y...

Basically ANDALSO is the same as regular AND except that the first value
you are testing MUST be true to evaluate as true.
Again, no. (and this definition is different than your first
definition , but both are wrong).

According to the table given in the help file, what I said is correct.

No, the table's not the point here. Both 'And' and 'AndAlso' share
the same table. The problem above is the word "except", since in
both cases the first value MUST be true for the phrase to evaluate
as true. In other words, "the first value you are testing MUST
be true to evaluate as true" is true of both 'And' and 'AndAlso',
so the word "except" makes no sense here.

Now if you really understand this and there's just some grammatical
confusion, then no big deal. But you keep trying to point out
the And/AndAlso difference by saying something about the value
of 'X And Y' vs. 'X AndAlso Y', and that's just not the difference
between the two operators.

The first value you are testing must be true in order for it to
evaluate to true regarless of the second value.

Likewise the second value must be true in order for it to evaluate to
true regardless of the first value.

Those two combined is simply is a very longwinded way of simply
saying...

only when both values are true does it evaluate to true.

And the lines above are true of the 'And' operator as well, so that
hardly points out the difference between them.