invalid column name when my insert data is string,when i use int it works fine - c#-4.0

Question

When i replace EmerPacienti with PatientId it works fine, why happen that?
if (DropDownList3.SelectedItem.Value == "In-Pacient")
{
SqlDataAdapter Da = new SqlDataAdapter("select * from Ipacient where EmerPacienti=" + TextBox11.Text + "", cn);
//SqlCommandBuilder Cmd = new SqlCommandBuilder(Da);
DataSet Ds = new DataSet();
Da.Fill(Ds, "Ipacient");
GridView1.DataSource = Ds.Tables[0];
GridView1.DataBind();

Answer 1

Use sql parameters to prevent sql injection, then you also don't need to wrap it in apostrophes which is required on text columns. So this is much better:
using (var cn = new SqlConnection("insert connection string"))
using(var da = new SqlDataAdapter("select * from Ipacient where EmerPacienti=#EmerPacienti", cn))
{
da.SelectCommand.Parameters.Add("#EmerPacienti", SqlDbType.VarChar).Value = TextBox11.Text;
DataTable table = new DataTable();
da.Fill(table);
GridView1.DataSource = table;
GridView1.DataBind();
}
If it was an int-value use int.Parse/int.TryParse:
using (var cn = new SqlConnection("insert connection string"))
using(var da = new SqlDataAdapter("select * from Ipacient where PatientId=#PatientId", cn))
{
int patientId;
if (int.TryParse(TextBox11.Text, out patientId))
{
da.SelectCommand.Parameters.Add("#PatientId", SqlDbType.Int).Value = patientId;
// ...
}
}