Thanks for the reply!
I did what you told me and I added the following code:D = Serial.read() - '0'; // "-0" to convert ASSCI to the actual data But for some reason the program does this:
-It asks my data, I pass it for example 0
-It stores that data at the current address A
-But then it also stores 0xDD and 0xDA at addresses (A+1) and (A+2)
After a bit of think I realized what was wrong: The serial monitor first sends D, but I also passed "\n" and '\r' so it passes that too, 
So if anyone else has this problem, in the serial monitor there's a small box saying something like also send newline and carriage return set that to no newline.
Thanks for all the help, but I still got 1 question: Is it possible to write some sort of program that sends the data that it reads from some file through the serial port so that I don't have to type all the data in the serial monitor because that could save me a lot of time.