append text to lines in a CSV file

This question seems to have been asked a million times around the web, but I cannot find an answer which will work for me.

Basically, I have a CSV file which has a number of columns (say two). The program goes through each row in the CSV file, taking the first column value, then asks the user for the value to be placed in the second column. This is done on a handheld running Windows 6. I am developing using C#.

It seems a simple thing to do. But I cant seem to add text to a line.

I cant use OleDb, as System.Data.Oledb isnt in the .Net version I am using. I could use another CSV file, and when they complete each line, it writes it to another CSV file. But the problems with that are - The file thats produced at the end needs to contain EVERY line (so what if they pull the battery开发者_如何转开发s out half way). And what if they go back, to continue doing this another time, how will the program know where to start back from.

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For every row, open the output file, append the new row to it, and then close the output file. To restart, count the number of rows in the existing output file from the previous run, which will give you your starting in the input file (i.e., skip that number of rows in the input file).

Edit: right at the start, use System.IO.File.Copy to copy the input file to the output file, so you have all the file in case of failure. Now open the input file, read a line, convert it, use File.ReadAllLines to read ALL of the output file into an array, replace the line you have changed at the right index in the array, then use File.WriteAllLines to write out the new output file.

Something like this:

string inputFileName = ""; // Use a sensible file name.
string outputFileName = ""; // Use a sensible file name.
File.Copy(inputFileName, outputFileName, true);
using (StreamReader reader = new StreamReader(inputFileName))
{
    string line = null;
    int inputLinesIndex = 0;
    while ((line = reader.ReadLine()) != null)
    {
        string convertedLine = ConvertLine(line);
        string[] outputFileLines = File.ReadAllLines(outputFileName);
        if (inputLinesIndex < outputFileLines.Length)
        {
            outputFileLines[inputLinesIndex] = convertedLine;
            File.WriteAllLines(outputFileName, outputFileLines);
        }
        inputLinesIndex++;
    }
}