Operator Andalso (Short Circuit Conjunction)

Returns the short circuit-and (conjunction) of two numeric values

Syntax
   Declare Operator AndAlso ( ByRef lhs As T1, ByRef rhs As T2 ) As Ret

Usage
   result = lhs AndAlso rhs

Parameters
   lhs
      The left-hand side expression.
   T1
      Any numeric or boolean type.
   rhs
      The right-hand side expression.
   T2
      Any numeric or boolean type.
   Ret
      A numeric or boolean type (varies with T1 and T2).

Return Value
   Returns the short circuit-and (conjunction) of the two operands.

Description
   This operator evaluates the left hand side expression.  If the result is 
   zero, then zero is immediately returned.  If the result is nonzero then 
   the right hand side is evaluated, and the logical result from that is 
   returned.
   (for conversion of a boolean to an integer, false or true boolean value 
   becomes 0 or -1 integer value) 

   The truth table below demonstrates all combinations of a short 
   circuit-and operation, the '-' denotes that the operand is not 
   evaluated.

      +---------+---------+------+
      |Lhs Value|Rhs Value|Result|
      |0        |-        |0     |
      |nonzero  |0        |0     |
      |nonzero  |nonzero  |-1    |
      +---------+---------+------+

   Short-circuiting is performed - only expressions needed to calculate the 
   result are evaluated.  The left hand side lhs is evaluated first, and 
   only if it evaluates to non-zero (true) is the right hand side rhs also 
   evaluated.  If the left hand side evaluation lhs returns zero (false), 
   it is known that at that point that the overall condition is false, so 
   the right hand side rhs is not evaluated (skipped).

   The return type is almost always an Integer, of the value 0 or -1, 
   denoting false and true respectively. Except if the left and right-hand 
   side types are both Boolean, then the return type is also Boolean.

   This operator cannot be overloaded for user-defined types.

Example
   '' Using the ANDALSO operator to guard against array access
   '' when the index is out of range

   Dim As Integer isprime(1 To 10) = { _
      _ ' 1  2  3  4  5  6  7  8  9  10
         0, 1, 1, 0, 1, 0, 1, 0, 0, 0 _
      }

   Dim As Integer n
   Input "Enter a number between 1 and 10: ", n

   '' isprime() array will only be accessed if n is in range
   If (n >= 1 And n <= 10) AndAlso isprime(n) Then
      Print "n is prime"
   Else
      Print "n is not prime, or out of range"
   End If

Differences from QB
   * This operator was not available in QB.

See also
   * OrElse
   * And
   * Operator Truth Tables

