并非所有的代码路径都返回值.程序应该怎么改？

Question

  public int CheckUser()
        {
            if (this.tbxUserName.Text == "")
            {
                MessageBox.Show("用户名不能为空！", "错误");
            }
            else if (this.tbxPassWord.Text == "")
            {
                MessageBox.Show("密码不能为空！", "错误");
            }
            else
            {
                string str = System.Configuration.ConfigurationSettings.AppSettings["ConnectionString"];
                SqlConnection conn = new SqlConnection(str);
                SqlCommand cmd = new SqlCommand("Login", conn);                cmd.CommandType = CommandType.StoredProcedure;
                SqlParameter UserName = new SqlParameter("@username", SqlDbType.VarChar, 50);
                UserName.Value = this.tbxUserName.Text;
                cmd.Parameters.Add(UserName);                SqlParameter PassWord = new SqlParameter("@pwd", SqlDbType.VarChar, 50);
                UserName.Value = this.tbxPassWord.Text;
                cmd.Parameters.Add(PassWord);                SqlParameter sp = new SqlParameter("@return", SqlDbType.Int, 4);                sp.Direction = ParameterDirection.Output;
                cmd.Parameters.Add(sp);                try
                {
                    conn.Open();
                    cmd.ExecuteNonQuery();
                    conn.Close();
                    int n = (int)(sp.Value);
                    return n;
                }
                catch
                {
                    return 0;
                }
            }
        }
        private void button1_Click(object sender, EventArgs e)
        {
            if (CheckUser() > 0)
            {
                PicManager pic = new PicManager();
                pic.Show();
                this.Hide();
            }
            else
            {
                MessageBox.Show("用户名不能为空");
            }
        }

Answer 1

CheckUser()最后一个大括号之前写上一句：return 0;

Answer 2

        public int CheckUser() 
        { 
            if (this.tbxUserName.Text == "") 
            { 
                MessageBox.Show("用户名不能为空！", "错误"); 
            } 
            else if (this.tbxPassWord.Text == "") 
            { 
                MessageBox.Show("密码不能为空！", "错误"); 
            } 
            else 
            { 
                string str = System.Configuration.ConfigurationSettings.AppSettings["ConnectionString"]; 
                SqlConnection conn = new SqlConnection(str); 
                SqlCommand cmd = new SqlCommand("Login", conn);                 cmd.CommandType = CommandType.StoredProcedure; 
                SqlParameter UserName = new SqlParameter("@username", SqlDbType.VarChar, 50); 
                UserName.Value = this.tbxUserName.Text; 
                cmd.Parameters.Add(UserName);                 SqlParameter PassWord = new SqlParameter("@pwd", SqlDbType.VarChar, 50); 
                UserName.Value = this.tbxPassWord.Text; 
                cmd.Parameters.Add(PassWord);                 SqlParameter sp = new SqlParameter("@return", SqlDbType.Int, 4);                 sp.Direction = ParameterDirection.Output; 
                cmd.Parameters.Add(sp);                 try 
                { 
                    conn.Open(); 
                    cmd.ExecuteNonQuery(); 
                    conn.Close(); 
                    int n = (int)(sp.Value); 
                    return n; 
                } 
                catch 
                { 
                    return 0; 
                } 
            }            return 0;  // <---- 最后加上这句！
 
        } 

Answer 3

 MessageBox.Show("用户名不能为空！", "错误");
加上 return 0; MessageBox.Show("密码不能为空！", "错误"); 
加上 return 0;