How to convert varchar to datetime

Question

When I try to update the dates "The conversion of a varchar data type to a datetime data type resulted in an out-of-range value" error is occurred.  How can I fix this issue. 

 

c# code

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SqlConnection cs = new SqlConnection(ConfigurationManager.ConnectionStrings["travelConnectionString"].ConnectionString);
String str = "UPDATE [tbl_training_details] SET [service_agent_id] = '" +
ddlServiceAgentList.SelectedValue + "',[training_addmission_date] = '" + txtAddmissionDate.Text + "',[training_exam_date] = '" + txtExamDate.Text + "',[training_certificate_no] = '" + txtCertificateNo.Text + "',[training_certificate_date] = '" + txtCertificateDate.Text + "',[status_id] = '" + ddlStatus.SelectedValue + "',[comment] = '" + txtComment.Text + "'WHERE [passenger_id] = " + txtPassengerName.Text;
SqlCommand sc = new SqlCommand(str, cs);
cs.Open();
sc.ExecuteNonQuery();
cs.Close();

 str value I got from this code is 

 

str = "UPDATE [tbl_training_details] SET [service_agent_id] = '0',[training_addmission_date] = '29/09/2016',[training_exam_date] = '20/10/2016',[training_certificate_no] = '5rfde',[training_certificate_date] = '2/11/2016',[status_id] = '14',[comment] = '5gfds'WHERE [passenger_id] = 10413"

Thanks