Unreachable code detected

Question

I'm getting a "Unreachable code detected" message in Visual Studio at the point con.close() in my code below. Can you spot what I've done wrong?

private int chek1(String insert)
{
    OleDbConnection con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb");
    OleDbCommand com = new OleDbCommand("select count(*) from sn where sn='" + insert + "\'", con);           
    con.Open();

    int po = (int)com.ExecuteScalar();           
    if (po > 0)
        return 1;
    else
        return 0;
    con.Close();    
}

Answer 1

The function exits when you return 1 or 0 (when you return anything, but 1 or 0 in your case); so there's no way that con.Close() can be called.

In the code you've posted, you're guaranteed to return, since you have a return statement in both branches of your if-statement. If only one branch had a return statement, con.Close() could still be reached.

But you shouldn't be using Close that way anyway -- you should be using using statements.

using (OleDbConnection con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb"))
using (OleDbCommand com = new OleDbCommand("select count(*) from sn where sn='" + insert + "\'", con))
{
    con.Open();

    int po = (int)com.ExecuteScalar();           
    if (po > 0)
        return 1;
    else
        return 0;

    // con.Close and con.Dispose will be called automatically at the end of the using block
}      

Answer 2

Your code could be like this:

private int check(string sn)
{
    using (OleDbConnection connection = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb"))
    using (OleDbCommand command = connection.CreateCommand())          
    {
        command.CommandText = "SELECT COUNT(*) FROM sn WHERE sn=?";
        command.Parameters.Add("@sn", sn));
        con.Open();               
        return ((int)com.ExecuteScalar() > 0) ? 1 : 0;
    }
}