Question

    ...
    ...
    ...

            try
            {
                string Tags_collect;

                SqlDataReader Data1 = cmd.ExecuteReader(); 
                Data1.Read();
                lbl_q_title.Text = Data1["subject"].ToString();

               Data1.NextResult();


               while (Data1.Read())
               {
                   Tags_collect = Data1.GetString(0);
                   Tags_collect= Tags_collect+ Tags_collect;
               }

               lbl_tags.Text = Tags_collect;
    .....
    ....

   ....

not sure why i get this error
what do i miss?

Answer 1

The first time you assign to Tags_collect is inside the while (Data1.Read()) loop, which is not guaranteed to ever execute.

Fix this by initializing the variable when it’s declared:

string Tags_collect = string.Empty;

Better yet, use a StringBuilder instead of relying on repeated concatenations:

StringBuilder tags = new StringBuilder();
// ...
while (Data1.Read())
{
    string tag = Data1.GetString(0);
    sb.Append(tag);
    sb.Append(",");  // Separator
}
lbl_tags.Text = tags.ToString();

Concatenating a string to itself in a loop is very inefficient because strings are immutable, so each concatenation creates a brand-new instance. Using a StringBuilder prevents this by using a single buffer.