how to execute c program in notepad ?

You can write a C program in Notepad and compile it using any compiler (such as gcc or microsoft's vc) and although it may seem like a good place to start to learn C, its really not a great approach. Notepad lacks the keyword font coloring, bookmarking, automatic indentation, integration with auto-complete/fill programs, and many other features that make working with IDE's useful. Even when working with gcc in linux, you'd always want to use an editor that is smart enough to do some of these things for you.

So consider using one of the free available IDEs instead (Studio Express, CodeBlocks, Eclipse with CDT, NetBeans), there's a lot to choose from.