Not understand NULL

1. A help file said that var1 in IsNull(var1) should be a Variant type variable, but in an exmaple var1 is a textbox name.  var1 can be what type?
2. If var1 is a txtbox name, or other object name, what means by IsNull(var1) = True?
3. Can we assign Null to a variable other than the ones of Variant type?
learnAsked:
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traygreenConnect With a Mentor Commented:
1) VB will typecast the variable to Variant - so string etc are valid parameters
2)if you pass the name in as parameter var1 and it is null then will return true
3)Typically no.  You have to assign an empty string to a string not null, nor can you assign it to numeric types
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caraf_gCommented:
1 the reason why the parameter in IsNull is a variant is because you can put in any type of variable - string, integer etcetera.
2 hard to say - if, for example, the data is retrieved from a database using SQL, it means that the contents of the field in the database was NULL.
3 No
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traygreenCommented:
Sorry the answer #2 is incorrect - It will return false
Basically Null is returned when a variable pointer does not address memory.
In other languages you would use it (or nil) to destroy the address link between a variable and it's memory location.  
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learnAuthor Commented:
So you, experts, said
a) we can put any type as the parameter in IsNull(), VB take care of turnning them to Variant;
b) we can not assign Null to any type except Variant.
am I right?

I remember I wrote a code
    Dim s As String
    Print IsNull(s)
and got error message: using Null incurrect....
I will check this code again later.

Thanks a lot
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learnAuthor Commented:
Sorry, we should not get any error in the last code.
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