Convert A to 1 B to 2 ... Z to 26 and then AA to 27 AB to 28 ...

Question

Does any one have algorithm or logic to Convert A to 1 ,B to 2, ... ,Z to 26 and then ,AA to 27, AB to 28 etc.

Answer 1

Have a look at these

/// <summary>
/// 1 -> A<br/>
/// 2 -> B<br/>
/// 3 -> C<br/>
/// ...
/// </summary>
/// <param name="column"></param>
/// <returns></returns>
public static string ExcelColumnFromNumber(int column)
{
    string columnString = "";
    decimal columnNumber = column;
    while (columnNumber > 0)
    {
     decimal currentLetterNumber = (columnNumber - 1) % 26;
     char currentLetter = (char)(currentLetterNumber + 65);
     columnString = currentLetter + columnString;
     columnNumber = (columnNumber - (currentLetterNumber + 1)) / 26;
    }
    return columnString;
}

/// <summary>
/// A -> 1<br/>
/// B -> 2<br/>
/// C -> 3<br/>
/// ...
/// </summary>
/// <param name="column"></param>
/// <returns></returns>
public static int NumberFromExcelColumn(string column)
{
    int retVal = 0;
    string col = column.ToUpper();
    for (int iChar = col.Length - 1; iChar >= 0; iChar--)
    {
     char colPiece = col[iChar];
     int colNum = colPiece - 64;
     retVal = retVal + colNum * (int)Math.Pow(26, col.Length - (iChar + 1));
    }
    return retVal;
}

Answer 2

Here's a simple LINQ expression:

static int TextToNumber(this string text) {
    return text
        .Select(c => c - 'A' + 1)
        .Aggregate((sum, next) => sum*26 + next);
}

This test

Console.WriteLine(" A -> " + "A".TextToNumber());
Console.WriteLine(" B -> " + "B".TextToNumber());
Console.WriteLine(" Z -> " + "Z".TextToNumber());
Console.WriteLine("AA -> " + "AA".TextToNumber());
Console.WriteLine("AB -> " + "AB".TextToNumber());

will produce this output:

 A -> 1
 B -> 2
 Z -> 26
AA -> 27
AB -> 28

Update: Here's the same code but targetting .NET 2.0:

static int TextToNumber(string text) {
    int sum = 0;
    foreach (char c in text) {
        sum = sum*26 + c - 'A' + 1;
    }
    return sum;
}