getting error while reading more than one char in C#

Question

I am getting error while reading more than one char in below code.

Intially we were using single char. But, later some time, we used more than one char.

When we used more than one char, i am getting error.

I used many places like below code.

**

• Additional information: String must be exactly one character long.

**

char startY = char.Parse(Y_StartCol); //Excel Column "F"
char endY = char.Parse(Y_EndCol); // Excel Column "AZ" ==> Getting error if we used more than one char.

How to minimally change the code if we used more than one char or single char

Answer 1

Try the following where the extension method ExcelColumnName is for getting into double characters for column names as there are in Excel.

Mockup

public static class ExtensionMethods
{
    public static string ExcelColumnName(this int index)
    {
        var chars = new char[]
        {
            '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'
        };

        index -= 1;
        string columnName;
        var quotient = index / 26;

        if (quotient > 0)
        {
            columnName = ExcelColumnName(quotient) + chars[index % 26];
        }
        else
        {
            columnName = chars[index % 26].ToString();
        }
        return columnName;
    }

}

Form code

for (int index = 1; index < 100; index++)
{
    var value = index.ExcelColumnName();
    if (value.Length == 1)
    {
        Debug.WriteLine(value);
    }
    else
    {
        Debug.WriteLine($"\t{value}");
        foreach (var character in value)
        {
            Debug.WriteLine($"\t\t{char.Parse(character.ToString())}");                
        }
    }
}

Partial output

X
Y
Z
 AA
   A
   A
 AB
   A
   B
 AC
   A
   C
 AD
   A
   D
 AE
   A
   E
 AF
   A
   F

Answer 2

To convert Excel column name to number, check an example:

string column = "AZ";
int number = column
 .Reverse( )
 .Select( ( c, i ) => new { n = char.ToUpper( c ) - 'A' + 1, p = unchecked((int)Math.Pow( 26, i )) } )
 .Sum( d => d.n * d.p );

The result is 1 for ‘A’, 2 for ‘B’, 52 for ‘AZ’, etc.

Then you can obtain startY and endY from these numbers. What values do you expect from columns like "F" and "AZ"?