What is the safest way to make SQL queries in c#? [duplicate]

By using the SqlCommand and its child collection of parameters all the pain of checking for sql injection is taken away from you and will be handled by these classes.

Here is an example, taken from Here:

 private static void UpdateDemographics(Int32 customerID,
    string demoXml, string connectionString)
{
    // Update the demographics for a store, which is stored  
    // in an xml column.  
    string commandText = "UPDATE Sales.Store SET Demographics = @demographics "
        + "WHERE CustomerID = @ID;";

    using (SqlConnection connection = new SqlConnection(connectionString))
    {
        SqlCommand command = new SqlCommand(commandText, connection);
        command.Parameters.Add("@ID", SqlDbType.Int);
        command.Parameters["@ID"].Value = customerID;

        // Use AddWithValue to assign Demographics. 
        // SQL Server will implicitly convert strings into XML.
        command.Parameters.AddWithValue("@demographics", demoXml);

        try
        {
            connection.Open();
            Int32 rowsAffected = command.ExecuteNonQuery();
            Console.WriteLine("RowsAffected: {0}", rowsAffected);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
    }