Operator ANDALSO (Short Circuit Conjunction)

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

declare operator AndAlso ( byref lhs as T1, byref rhs as T2 ) as Ret

result = lhs AndAlso rhs

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

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

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.

'' 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"
    Print "n is not prime, or out of range"
End If

Differences from QB:
See also:
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