AndAlso Operator (Visual Basic)
Performs short-circuiting logical conjunction on two expressions.
result = expression1 AndAlso expression2
A logical operation is said to be short-circuiting if the compiled code can bypass the evaluation of one expression depending on the result of another expression. If the result of the first expression evaluated determines the final result of the operation, there is no need to evaluate the second expression, because it cannot change the final result. Short-circuiting can improve performance if the bypassed expression is complex, or if it involves procedure calls.
If both expressions evaluate to
True. The following table illustrates how
result is determined.
||The value of
In a Boolean comparison, the
And operator always evaluates both expressions, which could include making procedure calls. The AndAlso Operator performs short-circuiting, which means that if
expression2 is not evaluated.
AndAlso operator is defined only for the Boolean Data Type. Visual Basic converts each operand as necessary to
Boolean before evaluating the expression. If you assign the result to a numeric type, Visual Basic converts it from
Boolean to that type such that
For more information, see Boolean Type Conversions.
The And Operator and the IsFalse Operator can be overloaded, which means that a class or structure can redefine their behavior when an operand has the type of that class or structure. Overloading the
IsFalse operators affects the behavior of the
AndAlso operator. If your code uses
AndAlso on a class or structure that overloads
IsFalse, be sure you understand their redefined behavior. For more information, see Operator Procedures.
The following example uses the
AndAlso operator to perform a logical conjunction on two expressions. The result is a
Boolean value that represents whether the entire conjoined expression is true. If the first expression is
False, the second is not evaluated.
Dim a As Integer = 10 Dim b As Integer = 8 Dim c As Integer = 6 Dim firstCheck, secondCheck, thirdCheck As Boolean firstCheck = a > b AndAlso b > c secondCheck = b > a AndAlso b > c thirdCheck = a > b AndAlso c > b
The preceding example produces results of
False, respectively. In the calculation of
secondCheck, the second expression is not evaluated because the first is already
False. However, the second expression is evaluated in the calculation of
The following example shows a
Function procedure that searches for a given value among the elements of an array. If the array is empty, or if the array length has been exceeded, the
While statement does not test the array element against the search value.
Public Function findValue(ByVal arr() As Double, ByVal searchValue As Double) As Double Dim i As Integer = 0 While i <= UBound(arr) AndAlso arr(i) <> searchValue ' If i is greater than UBound(arr), searchValue is not checked. i += 1 End While If i > UBound(arr) Then i = -1 Return i End Function