Editing a text file using visual C#

I had a text file log.txt and want to replace lines 3,6,9,12....... with "0". Suppose I have x no of lines in file "C:/log.txt", that is written using C#, and want to edit line no's that are divisible by 3 i.e 3,6,9,12,15.....,x.
Any Code?

 

Hi there,

Since you've written the file in C# I assume you already know how to open and write the actual text file. To find the row divisable by 3 when you loop through the lines in the file, use the modulus operator: %.

 

I had written the file using C# but unable to edit the specific lines.
Could you provide me the full code?
Plz

 

Here

int "line count"; //enter number of lines in txt file
StreamWriter sw = new StreamWriter("log.txt", true);
for (int i = 0; i < line count; i++)
{ 
   if (line count % 3 == 0)
         sw.WriteLine("0");
}
sw.Flush();
sw.Close();

Code (markup):

 

but it does not overwrite lines. it writes new lines.
I want to replace every third line.

 

This will work fine. It reads the contents of your file into an Arraylist, then writes it back out, missing out every 3rd row

            ArrayList al = new ArrayList();
            string filename = @"c:\log.txt";

            using (StreamReader sr = new StreamReader(filename))
            {
                string line;
                
                while ((line = sr.ReadLine()) != null)
                {
                    al.Add(line);
                }
                sr.Close();
            }

            using (StreamWriter sw = new StreamWriter(filename))
            {
                int lineCount = 1;

                foreach (String str in al)
                {
                    if (lineCount % 3 == 0)
                        sw.WriteLine("0");
                    else
                        sw.WriteLine(str);

                    ++lineCount;
                }
                sw.Close();
            }

Code (markup):