You need some help writing this code:
Here are some basic components for your program design. To simplify the matter, we'll use HW8.txt as input file, HW8.bin as binary output, and HW8c.txt as text output.
In "encoding.c", you have a function "encoding" which opens the text fiile "HW8.txt" for reading and the binary file "HW8.bin" for wrting. Then, read 4 characters at a time, pack them into an integer by a function "pack", manipulate the integer by "encryption", and write the encrypted integer into "HW8.bin" until the end of "HW8.txt". At the end of file, you may save some NULL ('\0') characters to make it 4 characters for the last integer. Close all open files.
In "decoding.c", you have a function "decoding" which opens "HW8.bin" for reading and a text file "HW8c.txt" for writing. Then, read an integer at a time, use the key from your partner to manipulate the integer by a function "decryption", unpack it into 4 characters by a function called "unpack", and save the 4 characters into "HW8c.txt". Close all open files.
The "encryption" function will shift an integer k bits to the left (or right) in circle in "encoding.c". Here k is the secrete key you share with your partner. The "decryption" will restore the encryption process in "decoding.c". That is, shifting k bits to the right (or left) in circle.
If you work in team, one person implement "encoding.c" and the other implement "decoding.c". You can give your header file and object file to your partner (encoding.h and encoding.o, or decoding.h and decoding.o), but not the source code. Your key and direction of circlic shift should be described and shared in the header file.
Presumably, you don't have your partner's "c" file, but you link the object file your partner provides, so your Makefile will be just using an existing object file for linking. Of course, you may just link with my object file. Then, you don't have a partner.
Your "main.c" is simple: display the content of "HW9.txt", call encoding, call decoding, and display the contents of "HW9c.txt". You can display the content of a file by a system call as follows, for example: system ("cat HW9.txt");
You should have the corresponding header file(s) for compilation. Again, you don't share your source code, but you share the header file(s) and the object files. The key is described in the header file(s).