How to make easy license protection to app?

In my experience if people want to pirate your game they're going to.

Even big companies with millions of bucks can't fully protect their games from piracy.

As Del_Duio says, you will never be able to make a bullet-proof system, it's just impossible especially on desktop apps. What you can do however, is make it as tricky and as complicated so Mr Joe Public will have a harder time figuring things out.

I really suggest at this point with you asking this question, you should play about with storing values in different places of memory (ie: multiple global values/alterable values) and changing which one to sync with in events. This will change the memory address at which the correct value is at.

Then you can test the file integrity with an MD5 check with your server online.

Wrap your executable into a wrapper... these are just a number of things you can do to make things hard work, but not fool-proof. If you wanted as much security as possible, you could make your app a "client shell" and liaise with an online server so you have a fully enabled server-client application, but then you would need to prevent people from 'sniffing' the packets, which is easy to do, so you would have to seriously obfuscate the data you are sending back and forth with handshakes, lots of salt and hashing. Even then, your app still wouldn't be 100%.

When it comes to security, each app is different. You have to imagine what you're capable of achieving in making things hard work for people who want to leak the app around. If you don't feel like you're ready for this yet, then now is the time to learn about all these topics. It just depends on how serious you are about security. It's a lot of hard work.