showing color in datagridview with the value of calendar

Question

I tried to fix my logical error in my datagridview. Here my code.

while (dr.Read())
{

    int id = dr.GetInt32(0);
    DateTime startBook = dr.GetDateTime(2);
    DateTime endBook = dr.GetDateTime(3);

    int startBook_C = startBook.Day;
    int endBook_C = endBook.Day;

    int TotalDays = endBook_C - startBook_C;

    //dataGridView1(startBook_C, id - 1).Style.BackColor = Color.Blue;
    dataGridView1.Rows[startBook_C].Cells[endBook_C-1].Style.BackColor = Color.Blue;
    int i;
    for (i = 1; i <= TotalDays; i++)
    {
        dataGridView1.Rows[startBook_C + i].Cells[endBook_C -1].Style.BackColor = Color.Blue;
        //dataGridView1.Rows[startBook_C].Cells[carID - 1].Style.BackColor = Color.Blue;
        // dataGridView1(startBook_C + i, id - 1).Style.BackColor = Color.Red;/* TODO ERROR: Skipped SkippedTokensTrivia */
        TotalDays -= 1;
    }
}
Con.Close();

I have a problem with datagridview, it's logical error and I don't know what is my error. I have an image below:

Answer 1

Consider startBook.Day= day 1 and endBook.Day = day 3 （ the row of ID 23). And the first loop i =1;

Then dataGridView1.Rows[startBook_C + i].Cells[endBook_C -1] is dataGridView1.Rows[**2**].Cells[**2**](start from 0) so the image provided shows DataGrid view table[3][3] is color blue .

For ID 23, the row is 0 (the first row). cell starts from 4 (the fifth, offset is 4, //ID+CARID+book StartDay+book EndDay=4.)

TotalDays -= 1; is not required in the loop.

while (dr.Read())
{
    int offset = 4;//ID+CARID+book StartDay+book EndDay=4.
    int id = dr.GetInt32(0);
    DateTime startBook = dr.GetDateTime(2);
    DateTime endBook = dr.GetDateTime(3);

    int startBook_C = startBook.Day;//1
    int endBook_C = endBook.Day;//3

    int TotalDays = endBook_C - startBook_C; //2
   
    for (int i = 0; i <= TotalDays; i++)
    {
       dataGridView1.Rows[0].Cells[offset+startBook_C - 1+i].Style.BackColor = Color.Blue;
      
    }

}
Con.Close();

Update: Since many methods in the examples do not provide clear definitions, I've provided my own way

int offset = 4;
foreach (DataGridViewRow row in dataGridView1.Rows)
{
   if (!row.IsNewRow)
   {

       if (row.Cells.Count >= 4)
       {

           DateTime startBook;
           DateTime endBook;
           if (DateTime.TryParse(row.Cells[2].Value?.ToString(), out startBook) &&
               DateTime.TryParse(row.Cells[3].Value?.ToString(), out endBook))
           {

               int startBook_C = startBook.Day;
               int endBook_C = endBook.Day;
               int TotalDays = endBook_C - startBook_C;
               for (int i = 0; i <= TotalDays; i++)
               {
                   dataGridView1.Rows[row.Index].Cells[offset + startBook_C - 1 + i].Style.BackColor = Color.Blue;

               }
           }
       }
   }
}