fixed wrong excel column name calculation

old/wrong: ExcelColumnName(77) >> "C@"
correct: "BZ"

Author: jochenwezel

ExcelOps/ExcelCommons/ExcelCell.vb

@@ -201,11 +201,16 @@
             Get
                 If columnIndex < 0 Then Throw New ArgumentOutOfRangeException(NameOf(columnIndex), "Must be a positive value")
                 Dim x As Integer = columnIndex + 1
-                If x >= 1 And x <= 26 Then
+                If x <= 26 Then
                     Return Chr(x + 64)
-                Else
-                    Return ExcelColumnName(CType(((x - x Mod 26) / 26), Integer) - 1) & Chr((x Mod 26) + 64)
                 End If
+                Dim quotient As Integer = x \ 26
+                Dim remainder As Integer = x Mod 26
+                If remainder = 0 Then
+                    remainder = 26
+                    quotient -= 1
+                End If
+                Return ExcelColumnName(quotient - 1) & Chr(remainder + 64)
             End Get
         End Property
 

ExcelOpsTest/DataTests/TextTableTest.vb

@@ -177,14 +177,20 @@ Namespace DataTests
         End Sub
 
         <Test> Public Sub ExcelColumnName()
-            Assert.AreEqual("A", TextTable.ExcelColumnName(0))
-            Assert.AreEqual("Z", TextTable.ExcelColumnName(25))
-            Assert.AreEqual("AA", TextTable.ExcelColumnName(26))
-            Assert.AreEqual("XFD", TextTable.ExcelColumnName(16383))
-            Assert.AreEqual("A", ExcelOps.ExcelCell.ExcelColumnName(0))
-            Assert.AreEqual("Z", ExcelOps.ExcelCell.ExcelColumnName(25))
-            Assert.AreEqual("AA", ExcelOps.ExcelCell.ExcelColumnName(26))
-            Assert.AreEqual("XFD", ExcelOps.ExcelCell.ExcelColumnName(16383))
+            Assert.Multiple(
+                Sub()
+                    Assert.AreEqual("A", TextTable.ExcelColumnName(0))
+                    Assert.AreEqual("Z", TextTable.ExcelColumnName(25))
+                    Assert.AreEqual("AA", TextTable.ExcelColumnName(26))
+                    Assert.AreEqual("XFD", TextTable.ExcelColumnName(16383))
+                    Assert.AreEqual("A", ExcelOps.ExcelCell.ExcelColumnName(0))
+                    Assert.AreEqual("Z", ExcelOps.ExcelCell.ExcelColumnName(25))
+                    Assert.AreEqual("AA", ExcelOps.ExcelCell.ExcelColumnName(26))
+                    Assert.AreEqual("XFD", ExcelOps.ExcelCell.ExcelColumnName(16383))
+                    Assert.AreEqual("BY", ExcelCell.ExcelColumnName(76)) 'Not: "C@"
+                    Assert.AreEqual("BZ", ExcelCell.ExcelColumnName(77)) 'Not: "C@"
+                    Assert.AreEqual("CA", ExcelCell.ExcelColumnName(78)) 'Not: "C@"
+                End Sub)
         End Sub
 
         <Test> Public Sub CellAddress()