Cannot use an If-statement with multiple conditions (AND/OR) when looping through variant array?

问题

Background:

In working with some variant arrays to sort data to multiple locations based on criteria, I noticed that using an if-statement with multiple criteria flagged as false every time. This was being used to create a dictionary, though it never made it to the dictionary aspect, due to the false response when looping only through the variant array.

I moved these to two separate if-statements and everything worked as expected.

Question:

Why am I unable to use a multi-condition if-statement when looping through data in a variant array?

Code in question:

General code to generate the variant array:

Public ex_arr As Variant, ex_lr As Long, ex_lc As Long
Public dc As Scripting.Dictionary 

Private Sub capture_export_array()
    With Sheets("export")
        ex_lc = .Cells(1, .Columns.Count).End(xlToLeft).Column
        ex_lr = .Cells(.Rows.Count, ex_lc).End(xlUp).Row
        ex_arr = .Range(.Cells(1, 1), .Cells(ex_lr, ex_lc)).Value
    End With
End Sub

Code that resulted in False conditions (immediate window print = 0):

Private Sub find_unique_items()
    Set dc = New Scripting.Dictionary
    Dim i As Long
    For i = LBound(ex_arr) To UBound(ex_arr)
        If InStr(ex_arr(i, ex_lc), "CriteriaA") And InStr(ex_arr(i, 4), "CriteriaB") Then dc(ex_arr(i, 2)) = ex_arr(i, 3)
    Next i
    Debug.Print dc.Count
End Sub

Code that resulted in desired output (immediate window print > 0):

Private Sub find_unique_items()
    Set dc = New Scripting.Dictionary
    Dim i As Long
    For i = LBound(ex_arr) To UBound(ex_arr)
        If InStr(ex_arr(i, ex_lc), "CriteriaA") Then
            If InStr(ex_arr(i, 4), "CriteriaB") Then dc(ex_arr(i, 2)) = ex_arr(i, 3)
        End If
    Next i
    Debug.Print dc.Count
End Sub

回答1:

InStr returns an index. As a logical operator, And wants to have Boolean operands. Given Integer operands, the And operator is a bitwise operator - truth be told, these operators are always bitwise; we just dub them "logical" operators when the operands are Boolean.

If InStr(ex_arr(i, ex_lc), "CriteriaA") Then

This condition is implicitly coercing the returned index into a Boolean expression, leveraging the fact that any non-zero value will convert to True.

Problems start when you bring logical/bitwise operators into the equation.

If InStr(ex_arr(i, ex_lc), "CriteriaA") And InStr(ex_arr(i, 4), "CriteriaB") Then dc(ex_arr(i, 2)) = ex_arr(i, 3)

Say the first InStr returns 2, and the second returns 1. The If expression becomes If 2 And 1 Then, so 0. That's zero, so the condition is false.

Wait, what?

Think of the binary representation of 2 vs that of 1:

  2:  0010
  1:  0001
AND:  0000

Bitwise-AND yields 0, since none of the bits line up.

Stop abusing implicit type conversions, and be explicit about what you really mean. What you mean to be doing, is this:

If (InStr(ex_arr(i, ex_lc), "CriteriaA") > 0) And (InStr(ex_arr(i, 4), "CriteriaB") > 0) Then dc(ex_arr(i, 2)) = ex_arr(i, 3)

(redundant parentheses for illustrative purposes only)

Now this evaluates two Boolean expressions, applies bitwise-AND to the two values, and correctly works as intended.

True: 1111
True: 1111
 AND: 1111

来源：https://stackoverflow.com/questions/57514747/cannot-use-an-if-statement-with-multiple-conditions-and-or-when-looping-throug

标签

excel

vba

loops

if-statement

variant-array