added the "main" section to the README

README.md

@@ -79,7 +79,22 @@ These structs all come with some library functions for ease of use, which allow
 ## main
 The driver code behind the program lives (obviously) in `main()`. 
 
-//TODO you were writing here
+The code is mostly found in the while loop, which runs until the value of `do_loop` is set to false, which only happens when the program reaches the EOF or the BUILTIN command exit is given. `inputLine` is the line that the user enters the shell. We declare `tokenList` to store all of the tokens that are picked up from the input. 
+
+`readInputLine()` reads the entire input line. We modified this function so that it returns NULL on EOF. Before we start, `inputLine` is quickly checked to see whether or not its NULL. If it is not, the function `getTokenList()` is run to extract all the tokens from the input and place them into `tokenList`.
+
+Since the `tokenList` will be edited, we create two copies of the list, `cpy` and `og`. Before looking through any tokens, the `parseInputList()` function is utilised to check the validity of `tokenList`. It is also checked whether or not the list is NULL. If these are both valid, we can begin executing the line, else we print an invalid syntax error message. 
+
+The execution is done within a while loop that runs until the `cpy` list is entirely consumed and is NULL. Within this while loop, we implemented a switch case which, at this level, should only accept the following enum types: 
+- EXECUTABLE
+- COMPOSITION
+- BUILTIN
+
+// TODO: discuss what the process is for each enum type.
+
+If the code encounters any other types at this level, it means that the syntax of the input is incorrect. If this happens, an error message is printed out and `cpy` is set to NULL in order to exit the loop.
+
+In the end, we use `free()` and `freeTokenList()` to free the memory.
 
 
 # bonuses