列RegNo，Name，Address，CreatedTime。在我的代码中遇到以下错误。

必须声明标量变量@RegNo 。

该怎么做。

当您创建参数化查询时 - 这正是执行SQL操作的正确方法 - 您还必须创建一个包含您希望传递给SQL的值的参数。这有点像在C＃中调用方法。你定义它

  public   int  DoInsert （ int  regNo， string  name， string 地址，日期时间insertDate）
 {
 ... 
} 

但是当你调用它时，你必须提供值：

int rowsAffected = DoInsert（ 666 ， Mike Smith， 2 Main Street，Kentucky，DateTime.Now）;

如果你遗漏了任何参数，就会出现编译错误。

SQL是一样的。

为每个参数添加一行：

 cmd.Parameters.AddWithValue（  @ NameOfParameterInSQLCommand，valueIWantInTheColumn ）; 

它将开始起作用。

protected void Add_Click(object sender, EventArgs e)
      {


          string constr = ConfigurationManager.ConnectionStrings["ApplicationServices"].ConnectionString;
          SqlConnection con = new SqlConnection(constr);
          //SqlCommand cmd = new SqlCommand("insert into Student values('" + RegNo.Text + "','" + Name.Text + "','" + Address.Text + "')");
          SqlCommand cmd = new SqlCommand("insert into Student(@RegNo,@Name,@Address,@CreatedTime) values(@RegNo,@Name,@Address,Getdate())");

          cmd.Connection = con;
          con.Open();

          cmd.ExecuteNonQuery();
          con.Close();

      }

What I have tried:

here am try to insert records . i have 3 textboxes namely RegNo,Name,Address and in my table I have $ columns RegNo,Name,Address,CreatedTime. in my code the following error encountered .
Must declare the scalar variable @RegNo .
what to do.

columns RegNo,Name,Address,CreatedTime. in my code the following error encountered .
Must declare the scalar variable @RegNo .
what to do.

When you create a parameterised query - and that is exactly the right way to do SQL operations - you have to also create a Parameter which contains teh value you wish to pass to SQL. It's a bit like calling a method in C#. You define it

public int DoInsert(int regNo, string name, string address, DateTime insertDate)
   {
   ...
   }

But when you call it, you must provide the values:

int rowsAffected = DoInsert(666, "Mike Smith", "2 Main Street, Kentucky", DateTime.Now);

If you miss out any parameters, you get a compiler error.
SQL is the same.
Add a line for each parameter:

cmd.Parameters.AddWithValue("@NameOfParameterInSQLCommand", valueIWantInTheColumn);

And it'll start to work.