String was not recognized as a valid DateTime.

Question

protected void btnrenew_Click(object sender, EventArgs e)

{

int P_Id = Convert.ToInt32(((Button)sender).CommandArgument.ToString());

SqlCommand cmd = new SqlCommand("Select Renew, Term From Plans where P_Id= '" + P_Id + "'", con);

SqlDataAdapter da = new SqlDataAdapter(cmd);

DataTable dt = new DataTable();

da.Fill(dt);

int RenewDate = Convert.ToDateTime(dt.Rows[0]["Renew"].ToString()).Day;

int RenewMonth = Convert.ToDateTime(dt.Rows[0]["Renew"].ToString()).Month;

int RenewYear = Convert.ToDateTime(dt.Rows[0]["Renew"].ToString()).Year;

int Term = Convert.ToInt32(dt.Rows[0]["Term"].ToString());

int TotalMonth = RenewMonth + Term;

if (TotalMonth <= 12)

{

string NextRenewDate = Convert.ToString(RenewDate.ToString("00") + "-" + TotalMonth.ToString("00") + "-" + RenewYear.ToString("00"));

SqlCommand cmd1 = new SqlCommand("Update Plans Set Renew=@Renew Where P_Id= '" + P_Id + "' ", con);

cmd1.Parameters.AddWithValue("@Renew", Convert.ToDateTime(NextRenewDate).ToString("yyyy/dd/MM"));

con.Open();

cmd1.ExecuteNonQuery();

con.Close();

ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "alertMessage", "alert('Your Policy RenewDate is Updated Successfully')", true);

displaydetail();

}

else if (TotalMonth > 24)

{

int NextRenewYear = RenewYear + 2;

int TotalMonth1 = (RenewMonth + Term) % 12;

string NextRenewDate1 = Convert.ToString(RenewDate.ToString("00") + "-" + TotalMonth1.ToString("00") + "-" + NextRenewYear.ToString("00"));

SqlCommand cmd1 = new SqlCommand("Update Plans Set Renew=@Renew Where P_Id = '" + P_Id + "' ", con);

cmd1.Parameters.AddWithValue("@Renew", Convert.ToDateTime(NextRenewDate1).ToString("yyyy/dd/MM"));

con.Open();

cmd1.ExecuteNonQuery();

con.Close();

ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "alertMessage", "alert('Your Policy RenewDate is Updated Successfully')", true);

displaydetail();

}

else if (TotalMonth > 12)

{

int NextRenewYear = RenewYear + 1;

int TotalMonth1 = (RenewMonth + Term) % 12;

string NextRenewDate1 = Convert.ToString(RenewDate.ToString("00") + "-" + TotalMonth1.ToString("00") + "-" + NextRenewYear.ToString("00"));

SqlCommand cmd1 = new SqlCommand("Update Plans Set Renew=@Renew Where P_Id = '" + P_Id + "' ", con);

cmd1.Parameters.AddWithValue("@Renew", Convert.ToDateTime(NextRenewDate1).Date);

con.Open();

cmd1.ExecuteNonQuery();

con.Close();

ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "alertMessage", "alert('Your Policy RenewDate is Updated Successfully')", true);

displaydetail();

}

else

{

}

}