Converting to Base 26 in One Based mode

Question

I needed to create a simple method that converts numbers in Base 26 (string) using, as expected, letters from a to z.

But that's not all, this Base 26 needs to be One Based. Which means that there is no representation for zero absolute value and there is a representation for 26 absolute value. Let me show a example:

In Base 26 Zero Based the number 18252 will be represented like:

$$ (18252)_{10} = (BBAA)_{26} $$

where B == 1 and A == 0. But as an One Based I need to get:

$$ (18252)_{10} = (ZYZ)_{26} $$

where Y == 25 and Z == 26.

So I came up with this snippet:

var array = new List<int>();
var div = myNumber;
var getOne = 0;
while (div > 26)
{
 var value = div % 26;
 value -= getOne;
 if (value <= 0)
 {
 value += 26;
 getOne = 1;
 }
 else
 {
 getOne = 0;
 }
 array.Add(value);
 div = div / 26;
}
div -= getOne;
if (div > 0) array.Add(div);
var letters = array.Select(s => (char)('A' + s - 1)).Reverse().ToArray();
return new string(letters);

Now I wonder if there is a better way write this.

• AlanT: It looks like you are trying to get an excel column name from a number e.g. 1 => A, 2 => B, ... 26 => Z, 27 => AA, 28 => AB. Is this correct? If so, are you happy with a solution that works as far as 16384 (the max number of columns in an Excel spreadsheet)?
• Jonny Piazzi: Yes, can be like Excel

Answer 1

You could slightly simplify the code as follows:

• Reduce the number of variables.
• Use the LinkedList<T> (and the AddFirst method) instead of the List<T> to eliminate reversion of array.
  Alternatively you can use the List<T>.Insert method to achieve the same result.

The code:

private static string ToBase26(int myNumber)
{
 var array = new LinkedList<int>();
 while (myNumber > 26)
 {
 int value = myNumber % 26;
 if (value == 0)
 {
 myNumber = myNumber / 26 - 1;
 array.AddFirst(26);
 }
 else
 {
 myNumber /= 26;
 array.AddFirst(value);
 }
 }
 if (myNumber > 0)
 {
 array.AddFirst(myNumber);
 }
 return new string(array.Select(s => (char)('A' + s - 1)).ToArray());
}

Answer 2

You could reduce the number of variables, and use LinkedList<T> method to eliminate reversion, like this:

private static string ToBase26(int number)
{
 var list = new LinkedList<int>();
 list.AddFirst((number - 1) % 26);
 while ((number = --number / 26 - 1) > 0) list.AddFirst(number % 26);
 return new string(list.Select(s => (char)(s + 65)).ToArray());
}

• Dmitry: This code doesn't even compile.
• somebody: What errors are it throwing?
• Dmitry: Try it yourself and see.
• Dmitry: And please perform some tests before posting. For instance, make sure that this code returns ZYZ for 18252.
• somebody: Fixed, and edited.