Select and Update within the same Store Procedure, and How to know if store procedure is successfully executed.

While Working on User Login Panel, I came across a situation where i have to update and select statement both in sp, but how would i know if these both statements are executed successfully.

CREATE PROC uspAppUserLogin
@AppUserEmail varchar(50),@AppUserPassword varchar(max),@AppUserID int OUT,@AppUsername Varchar(25) OUT,
@LastLoginDate varchar(20) out
AS
BEGIN
SET NOCOUNT ON; 
SELECT COUNT(*) FROM TblAppUser Where Email = @AppUserEmail and UserPassword =  @AppUserPassword
SET @AppUserID =(Select UserId  From TblAppUser Where Email = @AppUserEmail and UserPassword =  @AppUserPassword)
SET @AppUsername =(Select UserName From TblAppUser Where Email = @AppUserEmail and UserPassword =  @AppUserPassword)
SET @LastLoginDate = (Select ISNULL(LastLoginDate,GetDate()) From TblAppUser Where Email = @AppUserEmail and UserPassword =  @AppUserPassword)
Update TblAppUser Set LastLoginDate = GetDate() Where Email = @AppUserEmail and UserPassword =  @AppUserPassword
END

try
          {
              db1.sqlcmd = new SqlCommand("uspAppUserLogin");
              using (SqlDataAdapter sda = new SqlDataAdapter())
              {
                  db1.sqlcmd.CommandType = CommandType.StoredProcedure;
                  db1.sqlcmd.Parameters.AddWithValue("@AppUserEmail", TxtBxEmail.Text.Trim());
                  db1.sqlcmd.Parameters.AddWithValue("@AppUserPassword", hashpassword);
                  db1.sqlcmd.Parameters.Add("@AppUserID", SqlDbType.Int);
                  db1.sqlcmd.Parameters.Add("@AppUsername", SqlDbType.VarChar, 10);
                  db1.sqlcmd.Parameters.Add("@LastLoginDate", SqlDbType.VarChar, 20);
                  db1.sqlcmd.Parameters["@AppUserID"].Direction = ParameterDirection.Output;
                  db1.sqlcmd.Parameters["@AppUsername"].Direction = ParameterDirection.Output;
                  db1.sqlcmd.Parameters["@LastLoginDate"].Direction = ParameterDirection.Output;
                  db1.sqlcmd.Connection = db1.sqlcon;
                  db1.sqlcon.Open();
                  db1.sqlcmd.ExecuteNonQuery();
                  Userid = (int)db1.sqlcmd.Parameters["@AppUserID"].Value;
                  Username = (string)db1.sqlcmd.Parameters["@AppUsername"].Value;
                  recentlogin = (string)db1.sqlcmd.Parameters["@LastLoginDate"].Value;
              }
          }
          catch (Exception ex) { Response.Write(ex.Message); }
          finally
          {
              if (usercount == 1)  // comparing users from table 
              {
                  Session["AppUserName"] = Username;
                  Session["AppUserID"] = Userid;
                  Session["recentlogin"] = recentlogin;
                  Response.Redirect("HomeAppUser.aspx");  //for sucsseful login  
              }
              else
              {
                  db1.sqlcon.Close();
                  ClientScript.RegisterStartupScript(GetType(), "alert", "alert('" + "Invalid Login Details " + "');", true);
                  Response.Redirect("CandidateLogin.aspx");
              }
          }