I am trying to create a function which will give me alphabet position when an index is passed. It will be same like how excel shows it's columns. A...Z, AA,AB.... I wrote the below function to get the results upto Z. It looks like
static string GetColumnName(int index)
{
const int alphabetsCount = 26;
if (index <= alphabetsCount)
{
int code = (index - 1) + (int)'A';
return char.ConvertFromUtf32(code);
}
return string.Empty;
}
This works fine until 'Z'. It return 'A' if I pass 1 and return 'B' if I pass 2 and so on. But, I am not able to figure out how will I get AA when I pass 27 to this function. I guess I need a recursive method to find it.
Any inputs to this problem will be great!
Edit
This is suggested by Tordek. But his code will fail in numbers like 52, 78 etc. Added workaround for that and here is the final working code.
static string GetColumnName(int index)
{
const int alphabetsCount = 26;
if (index > alphabetsCount)
{
int mod = index % alphabetsCount;
int columnIndex = index / alphabetsCount;
// if mod is 0 (clearly divisible) we reached end of one combination. Something like AZ
if (mod == 0)
{
// reducing column index as index / alphabetsCount will give the next value and we will miss one column.
columnIndex -= 1;
// passing 0 to the function will return character '@' which is invalid
// mod should be the alphabets count. So it takes the last char in the alphabet.
mod = alphabetsCount;
}
return GetColumnName(columnIndex) + GetColumnName(mod);
}
else
{
int code = (index - 1) + (int)'A';
return char.ConvertFromUtf32(code);
}
}