c# - Convert A to 1 B to 2 ... Z to 26 and then AA to 27 AB to 28 (column indexes to column references in Excel)

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.

In other words, converting a column index into the column reference in Excel.

Answer 1

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;
}