问while循环中的值未更新

EN

while (r < dataTable.Rows.Count)    //get nearest value to the current target
{
    long nearest = long.MaxValue;
    long dtDiff = 0;
    while(nearest > dtDiff)
    {
      DateTime dtCurr = Convert.ToDateTime(dataTable.Rows[r][dtCol].ToString());
      dtDiff = Math.Abs(dtTarget.Ticks - dtCurr.Ticks);
      if(dtDiff < nearest)
      {
          Debug.WriteLine("Smaller value found r:" + r);
          Debug.WriteLine("diff:" + dtDiff.ToString() + " nearest:" + nearest);
          nearest = dtDiff;
          r++;
       }
       else
       {
          Debug.WriteLine("nearest value found " + r);
          long v = long.Parse(dataTable.Rows[r][dtCol + 1].ToString());
          values.Add(new NormValue { datetime = dt, value = v});
          dtTarget.AddSeconds(inc);
          break;
        }
    }
}