c# Add a Column to end of CSV file

Question

Trying to add a column to the end of a cvs file, which will just count up the number of lines (or can all be the same number it doesn\'t really mater) as the main aim is to

Answer 1

You should not index inside the foreach. The foreach gives you a line at a time.

lines.Skip(1).ToList().ForEach(line =>
{
    //-1 for header
    line += "," + newColumnData[index - 1];
    index++;
});

The lambda expression means: take each element in the list, and call it "line", and do what is inside the curly brackets to it.

Also, as I see it here, your newColumnData only seems to have one item in it, the string "D". Yet you are indexing it as if there was one item in this list for each line in the csv file you read. That too will cause an index out of range if your csv file has more than one line in it but... never mind, the more I think about it, the more you should just go with Dmitry Bychenko's answer.