列表中的项目计数未按预期工作

Question

I have a list which contains 91 items in it. I currently loop over and write each line to a text file using StreamWriter . I want to divide the list by 3 so after 30 items I want to insert a blank line. So far I have

foreach (var item in textList)
{
   //write to file
   counter++;
   if (counter == totalItems / 3)
   {
      await sw.WriteLineAsync(Environment.NewLine);
   }
}

but it only works for the first 30 items. Please note the list can contain any number of items but this particular one contains 91. However I will always have to divide into 3.

Answer 1

You either want to divide a list of 91 items by 3 or after 30 items. You can't have both. If you do it after every 30 items, you would have the 91st item separated from the rest, on its own 'chunk', i,e.1-30, 31-60, 61-90, 91. If you have 91 items, and want to split by 3, you should do it every 31 items (hence why I am using Math.Ceiling ). That way you'd have 1-31, 32-62 and 63-91.

Also, don't use foreach AND a counter; use the for loop instead. And you can use the modulus operator. As so:

int third = Convert.ToInt32(Math.Ceiling(textList.Count / 3.0));
int divider = third - 1;

for (int i = 0; i < textList.Count; i++)
{
    var itemToWrite = textList[i];
    //write to file

    if (i % third == divider) await sw.WriteLineAsync(Environment.NewLine);
}

Answer 2

Use modulo. Try like:

 if (counter % (totalItems / 3) == 0)
 {
   ...