IsInArray not returning True when it should - arrays

Question

I am using the IsInArray function to check if a cell address (Row,Column) exists within an array. For some reason, even though the array contains the value it doesn't match. For example if my array is like this:
18, 812, 84, 34, 412, 87, 74
And OldRow & OldCol gets to 34, the function IsInArray doesn't match it and execute Else.
Below is a sample of the code I am using to try and achieve this:
Set c = .Find(1, LookIn:=xlValues)
If Not c Is Nothing Then
firstAddress = c.Address
Do
cellAddress = c.Address
OldRow = Range(cellAddress).Row
OldCol = Range(cellAddress).Column
If IsInArray("OldRow & OldCol", mappedcells) = False Then
oldmappingrow = Application.Match(OldRow, Worksheets(1).Range("r3:r16"), 0)
If Not IsError(oldmappingrow) Then
OldRowMapped = Worksheets(1).Range("r3:r16").Cells(oldmappingrow).Offset(, 1).Value
End If
oldmappingcol = Application.Match(OldCol, Worksheets(1).Range("r3:r16"), 0)
If Not IsError(oldmappingcol) Then
OldColMapped = Worksheets(1).Range("r3:r16").Cells(oldmappingcol).Offset(, 1).Value
End If
If OldCol > OldRow Then
NewCol = WorksheetFunction.Max(OldRowMapped, OldColMapped)
NewRow = WorksheetFunction.Min(OldRowMapped, OldColMapped)
Else
NewRow = WorksheetFunction.Max(OldRowMapped, OldColMapped)
NewCol = WorksheetFunction.Min(OldRowMapped, OldColMapped)
End If
.Cells(NewRow, NewCol) = .Cells(OldRow, OldCol).Value
.Cells(OldRow, OldCol).Value = "0"
ReDim Preserve mappedcells(UBound(mappedcells) + 1) 'Add next array element
mappedcells(UBound(mappedcells)) = NewRow & NewCol 'Assign the array element
Set c = .FindNext(c)
Debug.Print (OldRow & OldCol & " moved to " & NewRow & NewCol)
Else
Set c = .FindNext(c)
End If
Loop While Not c Is Nothing And c.Address <> firstAddress
End If
And the IsInArray function I am using:
Function IsInArray(stringToBeFound As String, arr As Variant) As Boolean
IsInArray = Not IsError(Application.Match(stringToBeFound, arr, 0))
End Function
Sorry if the code is messy and could be written cleaner, I am totally new to vba and programming as a whole. Any help would be much appreciated!

Answer 1

"3" & "4" <> 34 but "3" & "4" = "34" and Int("3" & "4") = 34. Try it as,
If not IsInArray(clng(OldRow & OldCol), mappedcells) Then
As noted in the comment from Scott Craner below, go through your code and make sure you are comparing numbers to numbers or text to text and not numbers to text-that-looks-like-a-number.