VBScript logical operator
VBScript logical operators allow you to combine operations done by comparison operators to make "compound" If
statements, among other things. Logical operators take in two (or one) Boolean values and return another Boolean value.
Contents
Logical conjunction operator: And
The logical And
operator results in True only if both operands are True. In any other case, And
will return False.
If A And B Then AddQ "Variable A and variable B equal True." End If
For example, to combine embedded If
blocks:
If IsOnline() Then If myUsername <> "Bob" Then Disconnect End If End If
Becomes:
If IsOnline() And MyUsername <> "Bob" Then Disconnect End If
The IsOnline function returns a Boolean and so does the <>
operator.
Logical disjunction operator: Or
The logical Or
operator results in True when either of the two operands are True. Only when both are False will Or
return False.
If A Or B Then AddQ "Either variable A or variable B equals True." End If
Logical negation operator: Not
The logical Not
operator results in the opposite Boolean value of the single operand. Unlike other operators, Not
only takes one operator to its right (it is a "unary" operator).
If Not A Then AddQ "Variable A equals False." End If
For example, if we are not online, give an error:
If Not IsOnline() Then AddChat vbRed, "The bot cannot perform that function; it is offline." End If
Bitwise mistake
A common mistake made is due to VBScript's tendency to "implicitly", or silently, correct variable type problems. If, for example, one takes the result of the builtin InStr() function (an integer result) and puts it in an If
block:
If InStr("string", "s") Then AddQ "'s' is in 'string'." End If
The integer type will be converted to a Boolean type silently, since If
only takes a Boolean. If the function succeeds, it will return the index of the substring which is always greater than 0. Anything not equal to 0 will be converted to the Boolean True. If the function fails, it will return 0 which will be converted to False.
If Not InStr("string", "s") Then AddQ "'s' is not in 'string' (this may be the incorrect result)." End If
If the user then tries to use the Not
operator on the above, we will get the incorrect result because now we are invoking the bitwise Not
operator which acts when the operand is an integer.
It is more correct to do the following instead:
If InStr("string", "s") > 0 Then AddQ "'s' is in 'string'." End If If InStr("string", "s") = 0 Then AddQ "'s' is not in 'string'." End If
Logical exclusion operator: Xor
The logical Xor
operator (exclusive or) results in True only when one of the two operands are True. When both are True or both are False, the result is False.
If A Xor B Then AddQ "Variable A equals True and variable B equals False, or variable A equals False and variable B equals True." End If
This acts the same as:
If (A Or B) And Not (A And B) Then AddQ "Variable A equals True and variable B equals False, or variable A equals False and variable B equals True." End If
Logical equivalence operator: Eqv
The logical Eqv
operator ("equivalence") results in True when both operands are True or both operands are False. If one operand is True and the other is False, Eqv
returns False.
If A Eqv B Then AddQ "Variable A is equivalent to variable B." End If
This acts the same as:
If (A And B) Xor Not (A And B) Then AddQ "Variable A is equivalent to variable B." End If
Logical implication operator: Imp
The logical Imp
operator results in True in all cases when the second operand is True and when both operands are False. It results in False only when the first operand is True and the second is False.
If A Imp B Then AddQ "Variable A equals variable B or variable A equals False and variable B equals True." End If
This acts the same as:
If (A Eqv B) Or (Not A And B) Then AddQ "Variable A equals variable B or variable A equals False and variable B equals True." End If
Summary
First Operand  Operator  Second Operand  Result 

And :
 
True  And

True  True 
True  And

False  False 
False  And

True  False 
False  And

False  False 
Or :
 
True  Or

True  True 
True  Or

False  True 
False  Or

True  True 
False  Or

False  False 
Not :
 
Not

True  False  
Not

False  True  
Xor :
 
True  Xor

True  False 
True  Xor

False  True 
False  Xor

True  True 
False  Xor

False  False 
Eqv :
 
True  Eqv

True  True 
True  Eqv

False  False 
False  Eqv

True  False 
False  Eqv

False  True 
Imp :
 
True  Imp

True  True 
True  Imp

False  False 
False  Imp

True  True 
False  Imp

False  True 