Hmm, that made things more clear to me. Thank you all. I have tested HxD, but couldn't do much. I could change a string of my own test program that I made. In other programs I just couldn't find the strings that I saw on them in the hex editor. Actually I don't have many programs to test here in this PC. Also, paradigm shifter, I couldn't implement that function in the link you've passed. I've included the windows.h library and all but the code didn't compile. Guess I'll take a better look at it some time.
Anyway, three more questions that came to my mind:
1- The memory address allocated to things don't always change every time you run your programs? How text editors change memory values and when you execute the program these values are the right ones?
2- Isn't it possible to change memory and get the desired effects at run-time? Hex editors don't do that.
3- Isn't it possible to do the things you do on hex editor on your code? so you can automate stuff?