write list items based on count

Question

I have a list of items (lets says 30 strings); I'm trying to figure out how to write to a txt file 5 items, then new line, next 5 items, etc. Like this:

List<string> blah;
//List contains:
1
2
3
4
5
6
7
8
9
10

I want to write to a txt file so it looks like this:

1   2   3   4   5
6   7   8   9   10

I can't seem to figure out a counter that will write this. I'm using StreamWriter if that matters.

EDIT: This is what I have currently but only writes blank lines.

for (var a = 0; a < ls.Count; a++)
        {
            foreach (string s in ls)
            {
                if (a == 0)
                {
                    sr.Write(s);
                }
                else if((a % 5) == 0)
                {
                    sr.Write(s);
                    sr.Write("\t");
                }

            }
        }

This is driving me nuts because I know it a simple counter I need to basically say "after you write 5 items, start new line."

Answer 1

In pseudo code

for (int i = 0; i < list.Count; i++) {
    if (i == 0) {
        append to empty file (value)
    } else if ((i % 5) == 0) {
        append to new line (CR LF + value)
    } else {
        append to current line ("spaces or tab" + value)
    }
}

Answer 2

        StringBuilder sb = new StringBulder();

        for (int i = 0; i < blah.Count; i++)
        {
            sb.Append(blah[i].ToString());

            if (i % 5 == 0)
            {
                sb.AppendLine();
            }
            else
            {
                sb.Append(" ");
            }
        }

Answer 3

Expanding on JohnP's comment:

for(var i = 0; i < blah.Count; i++)
{
    if(i % 5 == 0)
        //do new line

    YourPrintFunction(i);
}

Answer 4

With LINQ:

StringBuilder sb = new StringBuilder();
int i = 0;

blah.ForEach(s => { if ((++i % 5) == 0) sb.AppendLine(s); else sb.Append(s + "\t"); });

File.WriteAllText("filename", sb.ToString());