NCL has a default graphics environment. If you wish your default graphics environment to be different then you should establish a .hluresfile in your home directory. NCL always looks to see if this file exists before doing any graphics. The file should be located in the home directory of the machine you are running on. A downloadable copy of the above reference pages.
Interactive mode is avaiable by entering ncl and hitting the return key.
At this point, individual NCL commands can be entered and executed by hitting the return key. You don't need a loop. Avoid do loops as much as possible. Dimensions in NCL follow C conventions.