ExecuteScalar() is of type object:
see here[
^]
so:
[webmethod]
public object getdep(int x)
{
using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["myconnection"].ConnectionString))
{
SqlCommand cmd = new SqlCommand("select depname from dep where depid="+x, connection);
connection.Open();
var result = cmd.ExecuteScalar();
return result;
}
}