How can I append my own exe to upgrade it with c programming. I have tried to use append mode in exe but helpless with it. Any way to modify any exe? There are simpler process for .txt but none for .exe.
I want to add the codes or join the functions just like any program updates.
It's not that simple. You can't (simply) add code to the end of an .exe file to modify it; there are internal indexes, tables, etc.
For software update you need to replace the file in question with a newer versions. There are frameworks for doing that in an easy and automated way. If you tell is what language and environment you are using, someone is sure to recommend a good software update solution.