Operator Andalso (Short Circuit Conjunction)operator

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

Operatorsoperatordocumented

Syntax

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

Parameters

Name		Description
`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	(not evaluated)	0
nonzero	0	0
nonzero	nonzero	-1

AndAlso equivalent to:
Iif( Lhs <> 0, Rhs <> 0, 0 )

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.

Remarks

Usage



result = lhs AndAlso rhs

Differences from QB

This operator was not available in QB.

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    (2, 3, 5 and 7 are the only prime numbers)

        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

Sleep

Reference

Documented in KeyPgOpAndAlso.html