Check out example codes for "c# get excel column number from letter". It will help you in understanding the concepts better.

Code Example 1

public static int ColumnNameToIndex(string name)
{
  var upperCaseName = name.ToUpper();
  var number = 0;
  var pow = 1;
  for (var i = upperCaseName.Length - 1; i >= 0; i--)
  {
    number += (upperCaseName[i] - 'A' + 1) * pow;
    pow *= 26;
  }

  return number;
}

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