要哭、求指教“System.Data.SqlClient.SqlException”类型的未经处理的错误在 System.Data.dll 中发生

要哭、求指教“System.Data.SqlClient.SqlException”类型的未经处理的异常在 System.Data.dll 中发生
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
                  SqlConnection con = new SqlConnection("server=.;database=dingdan;Integrated Security=True");
                con.Open();
                string str = "select*from user where UseId='"+ textBox1.Text +"'and pwd=+'"+ textBox2.Text+ "'";
                SqlCommand com = new SqlCommand(str, con);
                SqlDataReader sda =  com.ExecuteReader();
                if (sda.Read())


                {
                    con.Close();
                    Form2 Form2 = new Form2();
                    this.Hide();
                    Form2.Show();
                    
                }
                else
                {
                    MessageBox.Show("用户名或者密码错误");
                }
            }
        }
    }

————————————————————
未处理System.Data.SqlClient.SqlException
  HResult=-2146232060
  Message=关键字 'user' 附近有语法错误。
  Source=.Net SqlClient Data Provider
  ErrorCode=-2146232060
  Class=15
  LineNumber=1
  Number=156
  Procedure=""
  Server=.
  State=1
  StackTrace:
       在 System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
       在 System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
       在 System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
       在 System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
       在 System.Data.SqlClient.SqlDataReader.TryConsumeMetaData()
       在 System.Data.SqlClient.SqlDataReader.get_MetaData()
       在 System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
       在 System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds)
       在 System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)