vim talk.
 

How do i set vim default to have ":set nu"(line numbers) and shape the C program file in proper look?

Look at "locate vimrc". There should be a sample vimrc file that you can copy to ~/.vimrc. This setting will recognize a .c file and set the indentation appropriately. Edit the file to add the :set nu.

You could also edit the c.vim file to add the 'nu' option.

I think need more time to study that file.....It's complicating

One of the recent LXer posts on this site had a link to a "dotfiles" site that has a collection of useful .dot file including vim files. Look in the Syndication forum. They might be useful.

Simply copying the .vimrc_sample file to ~/.vimrc will give you everything you want except for setting the :nu option. There is a subdirectory that contains names like bash.vim, c.vim, etc. This is the file that the .vimrc file includes if vim detects a C source file.
You could (make a backup first) edit that file to make the change system wide for C source files.

Of course, if you haven't already, you should take a look at the
Vim documentation -- yes, it actually has documentation! To get to it, enter ":help" after you've started Vim. Of course, there's tons more, and even in user-friendly formatting, if you follow the link that says "Documentation" (gasp!) from Vim's web site.