loop problem.

Vulpes,

Sorry for i didn't put my question properly before. But, i would like to tell you that, i have found my mistake. There was a little iteration and incrementing problem. I have solved it.

Here, the codes modified:

int j = 0;
var csv = new StringBuilder();
for (int i = 0; i <= terms.Length; i++)
{
        if (terms[i] == firstlistA[j])
        {
                string first = terms[i];
                string second = firstlistB[j];
                j++;
                var newLine = string.Format("{0},{1}{2}", first, second, Environment.NewLine);                 csv.Append(newLine);
                }
                else
                {
                        string first = terms[i];
                        string second = "0";
                        var newLine = string.Format("{0},{1}{2}", first, second,                                                  Environment.NewLine);
                        csv.Append(newLine);
                }
                File.WriteAllText(sfd.FileName, csv.ToString());
}

It's difficult to say without knowing what's in the terms, firstlistA and firstlistB arrays.

However, what is clear is that if terms contains nothing but "0" after a certain point and firstlistA contains no "0" after that point, then the 'else' block will apply and the file will be filled with 0,0 lines from that point onwards.