You can build your app as one big EXE without any calls to any external libraries. (API & DLL are basically libraries of pre-made functions.) However you often end up re-writing functions that are already well written by someone else. My apps use very few API calls, and could probably do without them, (but I would give up the ability to easily do things like be able to tell if a previous instance of my app is running when a user starts the app).

Third party libraries (OCX's, DLL's, etc.) on the other hand is a different issue. I use those extensively. Why would I re-write (debug, etc.,) a complex set of routines when I can purchase them from a third party vendor?

Another important fact to consider is that if you build your app as one all-inclusive EXE you limit your ability to easily scale and maintain your app. It is recommended that modern apps be built as at least 3 tiers (presentation, business and database layers). Your tiers should each consist of distinct encapsulated components. (So you can modify individual components when necessary without breaking the app.) Fixes to a component requires that you redeploy only the affected component rather that the entire app. It is difficult to build you app like this and deploy it enterprise wide without using COM components (usually DLLs).

>That mean .. API is not a must in the application .. correct ?
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>is't the same case for DLL, ED?
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>Your help is highly appreciated