You have the code snippet, look at the definition of main. The args parameter is set by the framework as an array of strings which correspond to the parameters on the command line. Unrequited desire is character building. OriginalGriff I'm sitting here giving you a standing ovation - Len Goodman

For text data, look for lines that don't contain an embedded space, then append " 0": public List<string> CleanupText(List<string> inputLines) { List<string> outputLines = new List<string>(); foreach (string s in inputLines) { // Note: the Trim() and Replace() ensure that (a) there are no false hits and (b) no false misses, respectively if (s.Trim().Replace('\\t', ' ').Contains(" ")) outputLines.Add(s); else outputLines.Add(string.Concat(s, " 0")); } return outputLines; } If you want to modify the collection in place, you'll have to replace the foreach() with a for() and an index into the list - since foreach() loops disallow modifying the collection they are iterating. To do this with Excel you'll have to iterate rows (the end condition being a cell in the first column that is empty), looking for cells in the 2nd column that are blank and inserting a '0' into those blank cells. I've not done enough MSOffice interop to be able to give you a code example.