C#中typeof(string)

Question

private void InitReport()
{
string str = "select autoPeriod from Setting";
DataTable dts = SQLServer.SQLInquiry(str);
string strAutoPeriodId = "-1"; // 默认权限

if (dts.Rows.Count == 1)
{
strAutoPeriodId = dts.Rows[0][0].ToString().Trim();
}

string strSql = "select * from Period";
DataTable dt = SQLServer.SQLInquiry(strSql);
dt.Columns.Add("strWeek1", typeof(string));
dt.Columns.Add("strWeek2", typeof(string));
dt.Columns.Add("strWeek3", typeof(string));
dt.Columns.Add("strWeek4", typeof(string));
dt.Columns.Add("strWeek5", typeof(string));
dt.Columns.Add("strWeek6", typeof(string));
dt.Columns.Add("strWeek7", typeof(string));
dt.Columns.Add("IsAuto", typeof(string));

// 处理星期, true为√ false为×
int nRow = dt.Rows.Count;
for (int i = 0; i < nRow; i++)
{
DataRow dtr = dt.Rows[i];
for (int j = 0; j < 7; j++)
{
bool bIsCheck = Convert.ToBoolean(dtr[4 + j]);
if (bIsCheck)
{
dtr[13 + j] = "√";
}
else
{
dtr[13 + j] = "×";
}
}
if (dtr["periodId"].ToString().Trim() == strAutoPeriodId)
{
dtr["IsAuto"] = "★";
}
}

rptPeriodList.DataSource = dt;
rptPeriodList.DataBind();
}
能解释13是怎么来的吗，4是第5列属性
表中属性依次为periodId,name,datetimeStart,datetimeEnd,Monday,Tuesday,Wednesday,
Thursday,Friday,Saturday,Sunday,timeBegin,timeEnd

Answer 1

Period 表里按列的索引排下去是这样的：
0:periodId ,1:name,2:datetimeStart,3: datetimeEnd, 4:Monday, 5:Tuesday, 6:Wednesday,
7:Thursday, 8:Friday, 9: Saturday, 10:Sunday, 11:timeBegin, 12:timeEnd

dt.Columns.Add("strWeek1", typeof(string)); 这句话的意思是向Period里添加新的列，列名为strWeek1，类型是string。所以加完以后多出来的列如下：
13:strWeek1,14:strWeek2, .... , 19: strWeek7, 20:IsAuto

现在知道13怎么出来的了吧？

Answer 2

楼上好详细……