UDK is the compiled ready to use Unreal engine3.
It's a development platform, for creating games (geared towards 3d).
Many games have been made on the Unreal Engines, (note: not udk):
Gears of War series, Splintercell series, Rainbow Six Vegas series, Unreal series, Unreal tournament series, Batman Arkham asylum, and many many more.
UDk, since it does not provide the sourcecode, should be able to mimic/utilize some or even in some cases all aspects of many of these games, for your own game project, using UnrealScript/Kismet, and tools provided. But for some aspects you need sourcecode, which is only available with the Full license of the Unreal Engine 3, which is not the UDK license, but a far more expensive one.
Depending on your project needs, you can achieve everything with the UDK provided features (aka, tools, Unrealscript)
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so thanks my dear for answer.i hav eanother question:
1.what is MOD?wna who is moder?
2.why someones says making games in UDK is mod?
3.where is editor in UDk for scripting?
thanks a lot.
1. A Mod with the context of video games is generally a modification of a video game to change or add elements to create new features or gameplay. Basically anything a user/player adds to a game that was not intended for my the developers is a mod.
2. Generally you make games in UDK by extending code in UDK which a lot of the time is the similar code of used in UT3. So I can see why some may say that is like modding. However you can completely rewrite that UT code to suite your game however you like.