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Must declare the scalar variable #empname

Getting Error in Csharp :
string sq = "select EmpName,contactnumber,dob,Address from tbl_emp_details where empname = #empname";
SqlCommand cmd = new SqlCommand(sq, con);
cmd.Parameters.AddWithValue("#empname", comboBox1.SelectedText);
SqlDataAdapter adp = new SqlDataAdapter(sq, con);
// com.Parameters.AddWithValue("#empname",Name.SelectedText);
DataTable dt = new DataTable();
adp.Fill(dt);
Name.Text = dt.Rows[0]["Empname"].ToString();

You're creating the data adapter using the original SQL and not the command (which includes the parameter) that you create.
Change
SqlDataAdapter adp = new SqlDataAdapter(sq, con);
to
SqlDataAdapter adp = new SqlDataAdapter(cmd);

Database update error with SQL Server 2012 and C#

I am trying to update my data in a SQL Server database through C#. I am getting updated. But the problem is the data is updated twice.
For example I have 10 (int) in my balance and if I add another 10, it turns to 30.
Any help would be appreciated.
Here is my code:
protected void LoginClick(object sender, EventArgs e)
{
DataTable dr = new DataTable();
string email = txtEmail.Text;
SqlConnection con = new SqlConnection(Ws.Con);
con.Open();
int s = Convert.ToInt32(add.Text);
SqlCommand cmd = new SqlCommand("Update [Order] set Balance=Balance+'" + s + "',Card='" + card.Text + "' where email=#email ", con);
cmd.Parameters.AddWithValue("email", email);
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
sda.Fill(dt);
int i = cmd.ExecuteNonQuery();
con.Close();
}

I would like to rectify few mistakes in your code,
DataTable is not needed to execute the update query, ExecuteNonQuery will do the job
The adapter.Fill and ExecuteNonQuery do the same job here and that's why your updates happening twice
Make use of parameterization while dealing with user inputs to avoid exceptions
For parsing integers use int.TryParse instead for Convert.ToInt32
I think the following code would help you to do the same function in a smarter way:
int currentBalance = 0;
if(int.TryParse(txtAdd.Text, out currentBalance))
{
string querSql = "Update [Order] set Balance = Balance + #balance," +
" Card = #card where email = #email"
using (SqlConnection dbConn = new SqlConnection("connectionString here"))
{
dbConn.Open();
using (SqlCommand sqlCommand = new SqlCommand(querySql, dbConn))
{
sqlCommand.Parameters.Add("#balance", SqlDbType.int).value = currentBalance;
sqlCommand.Parameters.Add("#card", SqlDbType.VarChar).value = card.Text;
sqlCommand.Parameters.Add("#email", SqlDbType.VarChar).value = email;
sqlCommand.ExecuteNonQuery();
}
}
}
Please note: YOu are parsing the balance as an integer value, so I assume the column Balance is an integer field in the database, if not make use of corresponding datatype for the parameter #balance also update the parsing technique

As per the documentation:
SqlDataAdapter(SqlCommand)
Initializes a new instance of the SqlDataAdapter class with the specified SqlCommand as the SelectCommand property.
What is going wrong in your code?
Actually you are passing SqlDataAdapter your update query as the Select command. So now when you will use this instance of SqlDataAdapter to Fill your datatable then actually you are executing your Update command. Look at the following code along with comments to see what is going wrong:
DataTable dr = new DataTable();
string email = txtEmail.Text;
SqlConnection con = new SqlConnection(Ws.Con);
con.Open();
int s = Convert.ToInt32(add.Text);
SqlCommand cmd = new SqlCommand("Update [Order] set Balance=Balance+'" + s + "',Card='" + card.Text + "' where email=#email ", con);
cmd.Parameters.AddWithValue("email", email);
SqlDataAdapter sda = new SqlDataAdapter(cmd);//The Select command for SqlDataAdapter
//is actually now the update command specified by cmd instnace of SqlCommand
DataTable dt = new DataTable();
sda.Fill(dt);//here SqlDataAdapter will execute it's Select command which is actually set
//to an update statement so your record will be updated
int i = cmd.ExecuteNonQuery();//and here again the update command is being executed now
//directly using the SqlCommand cmd instance and thus your record gets updated twice
con.Close();
Fixed Code:
DataTable dr = new DataTable();
string email = txtEmail.Text;
SqlConnection con = new SqlConnection(Ws.Con);
con.Open();
int s = Convert.ToInt32(add.Text);
SqlCommand cmd = new SqlCommand("Update [Order] set Balance=Balance+'" + s + "',Card='" + card.Text + "' where email=#email ", con);
cmd.Parameters.AddWithValue("email", email);
//Create a new SqlComamnd
SqlCommand selectCommand = new SqlCommand("Select * from [Order]");
//Put the newly created instance as SelectCommand for your SqlDataAdapter
SqlDataAdapter sda = new SqlDataAdapter(selectCommand);
DataTable dt = new DataTable();
sda.Fill(dt);
int i = cmd.ExecuteNonQuery();
con.Close();
Hope this help and do have a look at the documentation for better understanding of the SqlDataAdapter and DataTable. Thanks.

ExecuteNonQuery: Connection property has not been initialized. c sharo

may be i am tired but any body can say what is the poblem?
SqlConnection conn = new SqlConnection(#"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename='c:\users\deltagare\documents\visual studio 2015\Projects\School\School\school.mdf';Integrated Security=True");
private void Form1_Load(object sender, EventArgs e)
{
// TODO: This line of code loads data into the 'schoolDataSet.student' table. You can move, or remove it, as needed.
//this.studentTableAdapter.Fill(this.schoolDataSet.student);
conn.Open();
SqlCommand cmd = new SqlCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = "select * from student";
cmd.ExecuteNonQuery();
DataTable dt = new DataTable();
student = new StudentController();
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(dt);
studentGridView.DataSource = dt;
conn.Close();
}

You have either to use the SqlCommand(string,SqlConnection) overload, or set the SqlCommand.Connection property:
SqlCommand cmd = new SqlCommand("select * from student",conn);
Or
cmd.Connection=conn;

you have to assign the connection to the command before you execute it:
cmd.Connection = conn

C# Error: "Fill: SelectCommand.Connection property has not been initialized."

I'm using this video to try and populate results from a DataGridView, and am receiving the above error. The below code pertains to this error - I pass values into a stored procedure, then the final SELECT returns the values in the table in the DataGridView.
SqlConnection con = new SqlConnection();
con.ConnectionString = "integrated security=SSPI;data source=SERV;" + "persist security info=False;initial catalog=DB";
con.Open();
SqlCommand select = new SqlCommand("SELECT * FROM Table");
SqlCommand enter = new SqlCommand("sp_Proc", con);
// Stored Procedure
enter.CommandType = CommandType.StoredProcedure;
enter.Parameters.Add(new SqlParameter("#vvalue", SqlDbType.VarChar)).Value = Convert.ToString(txt1.Text);
enter.Parameters.Add(new SqlParameter("#dvalue", SqlDbType.Decimal)).Value = Convert.ToDecimal(txt2.Text);
enter.ExecuteNonQuery();
// DataGrid returns the SELECT
SqlDataAdapter sadapt = new SqlDataAdapter(select);
sadapt.SelectCommand = select;
DataTable dtab = new DataTable();
sadapt.Fill(dtab); // generates the error
BindingSource b = new BindingSource();
b.DataSource = dtab;
dGrid.DataSource = b;
sadapt.Update(dtab);
con.Close();

You did not pass connection object on the command. Try this instead,
SqlCommand select = new SqlCommand("SELECT * FROM Table", con);

You are passing connection object to your enter command but didnt pass the connection object to your select command
SqlCommand select = new SqlCommand("SELECT * FROM Table");
SqlCommand enter = new SqlCommand("sp_Proc", con);
Use this
SqlCommand select = new SqlCommand("SELECT * FROM Table",con);

SqlCommand cmd = new SqlCommand("sp_StockAnalysis2") // connection missing in sqlcommand
SqlCommand cmd = new SqlCommand("sp_StockAnalysis2",Connection())// pass connection

SQL Error Must declare the scalar variable

private void FillInvoiceList()
{
DataTable distinctInvoice = new DataTable();
using (SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["APOS_CONNECTION_STRING"].ConnectionString))
{
conn.Open();
SqlCommand cmd = new SqlCommand("Select distinct svc_tag from data where rep_name = #value");
cmd.Parameters.AddWithValue("#value", this.DropDownList1.SelectedItem.Text);
SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(cmd.CommandText, conn.ConnectionString);
sqlDataAdapter.Fill(distinctInvoice);
}
foreach (DataRow row in distinctInvoice.Rows)
{
this.ListBox1.Items.Add(row["svc_tag_dim_invoice_num"].ToString());
}
}
I have this code and I get this error when I call the Fill(DistinctInvoice)
Must declare the scalar variable "#value"
My FillInvoiceList() Method is being called from a SelectedIndexChanged event from the DropDownList1. The value of DropDownList1.SelectedItem.Text seems to be correct.
Thanks for any help.

The error is here :
SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(cmd.CommandText, conn.ConnectionString);
You're setting the SQLDataAdapter to use the original CommandText, not the SQLCommand itself. Change it to :
SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(cmd, conn.ConnectionString);