# Useful Code Snippet for finding columns in Excel

Hi all,

I have been working on a project for a while now and needed a quick converter between an integer index and the column of an Excel spreadsheet, I couldn’t find a general algorithm, so had to write one…

At first I thought it was a simple base 26 (26 letters in the alphabet) system, but then realized that with the first column being indexed as 0 or 1 there would be an inconsistency when you get to the 26th column (where it should read “AA”, or “10” in a base 26 system), “A” is both representing the values 0 and 1.

I worked for a while on an algorithm to calculate the correct value and have come up with the following static class to do it:

**Converting between integer index and Column string:**

```
using System;
```

```
using System.Diagnostics;
```

```
/// <summary>
/// Converter from numberical index of column to the identifier in excel
/// </summary>
public static class Column
```

```
{
```

```
/// <summary>
```

```
/// Array of alphabet
```

```
/// </summary>
```

```
private static string[] alphabet = { "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z" };
```

```
/// <summary>
```

```
/// Converts from numberical index of column to the identifier in excel
```

```
/// </summary>
```

```
/// <param name="index">The index of the column</param>
```

```
/// <returns>The corrisponding letter string of that column</returns>
```

```
public static string Index(int index)
```

```
{
```

```
string value = string.Empty;
```

```
int Base = alphabet.Length;
```

```
int currentPower = 0;
```

```
if (index >= 0)
```

```
{
```

```
do
```

```
{
```

```
if (Math.Pow(Base, currentPower) < int.MaxValue)
```

```
{
```

```
value = alphabet[((index - RecursivePower(Base, currentPower)) / (int)Math.Pow(Base, currentPower)) % Base] + value;
```

```
currentPower++;
```

```
}
```

```
else
```

```
{
```

```
Trace.WriteLine("That index is too high for the value of MaxInt on this system, so can not continue");
```

```
return string.Empty;
```

```
}
```

```
}
```

```
while (RecursivePower(Base, currentPower) <= index);
```

```
}
```

```
return value;
```

```
}
```

```
/// <summary>
```

```
/// Do a recursive summing of powers from starting power to 1
```

```
/// </summary>
```

```
/// <param name="theBase"></param>
```

```
/// <param name="startingPower"></param>
```

```
/// <returns>The sum of the powers of theBase to 1 (0 if power starts > 1)</returns>
```

```
private static int RecursivePower(int theBase, int startingPower)
```

```
{
```

```
int value = 0;
```

```
for (int i = startingPower; i > 0; i--)
```

```
{
```

```
value += (int) Math.Pow(theBase, i);
```

```
}
```

```
return value;
```

```
}
```

```
}
```

I hope that helps anyone trying to do this… again it can be ported into VB if you want to script it, and remember where I used alphabet as an array you could always use Chr(*index calculation here* + 65) which I believe indexes the “A” character when 0 is added to it.