protected void Page_Load(object sender, EventArgs e)
{
    string str1, str2, s1 = "第一个参数", s2 = "第二个参数";

    //运行下面一行代码,会提示以下错误:
    //  使用了未赋值的局部变量“str1”
    //UseRef(ref str1, ref str2);

    //输出结果:
    //  使用out的第一个参数
    //  使用out的第二个参数
    UseOut(out str1, out str2);
    Response.Write(str1 + "<br/>");
    Response.Write(str2 + "<br/>");

    //输出结果:
    //  第一个参数使用ref
    //  第二个参数使用ref
    UseRef(ref s1, ref s2);
    Response.Write(s1 + "<br/>");
    Response.Write(s2 + "<br/>");
}

public void UseOut(out string str1, out string str2)
{
    str1 = "使用out的第一个参数";
    str2 = "使用out的第二个参数";
}

public void UseRef(ref string s1, ref string s2)
{
    s1 += "使用ref";
    s2 += "使用ref";
}

    ALTER PROCEDURE dbo.InsertEmployee
    (
        @EmployeeName nvarchar(20),
        @EmployeeAge int=null,
        @EmployeeDepartmentID int=null,
        @EmployeeScore int=null,
        @outValue nvarchar(20) output
    )

    AS
        /* SET NOCOUNT ON */
        if exists(select * from Employee where EmployeeName=@EmployeeName)
        begin
            set @outValue=‘用户名‘+@EmployeeName+‘重复!‘
            return
        end
        
        insert into Employee (EmployeeName,EmployeeAge,EmployeeDeparmentID,EmployeeScore)
        values (@EmployeeName,@EmployeeAge,@EmployeeDepartmentID,@EmployeeScore)
        
        set @outValue=‘用户‘+@EmployeeName+‘建立成功!‘
        
        return

string connectionString = ConfigurationManager.ConnectionStrings["dbstconnectionstring"].ConnectionString;

SqlConnection conn = new SqlConnection(connectionString);

SqlCommand cmd = conn.CreateCommand();

cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "InsertEmployee";

cmd.Parameters.AddWithValue("@EmployeeName", "宋八");
cmd.Parameters.AddWithValue("@EmployeeAge", 20);
cmd.Parameters.AddWithValue("@EmployeeDepartmentID", 1);
cmd.Parameters.AddWithValue("@EmployeeScore", 95);

//注意param_outValue.Direction
//      设置param_outValue.Direction=Output,参数只需被声明即可
//      对应数据库中output
//SqlParameter param_outValue = new SqlParameter("@outValue", SqlDbType.NVarChar, 20);
//param_outValue.Direction = ParameterDirection.Output;
//cmd.Parameters.Add(param_outValue);   

//注意param_outValue.Direction
//      设置为param_outValue.Direction=InputOutput,参数需要被初始化
//      对应数据库中output
SqlParameter param_outValue = new SqlParameter("@outValue", SqlDbType.NVarChar,20);
param_outValue.Direction = ParameterDirection.InputOutput;
param_outValue.Value = string.Empty;
cmd.Parameters.Add(param_outValue);  

conn.Open();
cmd.ExecuteNonQuery();
conn.Close();

Response.Write(param_outValue.Value);

用户宋八建立成功! 

用户名宋八重复!