Great C programming funHEADmaster

Excellent fundamentals and displine training, many tools and techniques
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+ In the last problem, you saw an implementation of a simple
+"encryption" program.  In this problem, you will write a program
+that breaks that encryption---that is, it will take as input
+a text file encrypted with the encryption program you just
+saw, and prints out the key used to encrypt it!
+
+Breaking the Caesar Cipher uses a technique called "frequency counting."
+This technique relies on the fact that the distribution of letters
+in the English alphabet is far from uniform: 'e' is by far the most
+common letter (~13%), followed by 't' (9%), and 'a' (8%).  Note
+that the average frequency is 100/26 ~= 4%. 
+
+This frequency distribution means that if you know (or suspect)
+that a file contains English text encrypted with a Caesar Cipher,
+you can simply count the frequency of all letters in it, and guess
+that the letter which occurs most often is 'e'.   Once you know
+which letter is 'e', you can backsolve for the key and decrypt
+the file.  Note that in practice this requires a large enough
+text that "the law of large numbers" applies---and while it is
+not guaranteed to work, it typically does.
+
+
+Requirements:
+=============
+
+ - Your program will take one command line argument: the name
+   of a file to read as input
+ - Your program will then perform frequency counting on the letters
+   in that text file.  Your program should ignore all non-letter
+   characters (those un-modified by your problem 1 program).
+ - Your program should use the frequency count information to 
+   determine which letter is 'e', and solve for the key.
+ - On success, your program should print a single line of output to
+   stdout, which should contain one decimal (base 10) integer (followed by a
+   newline character).  This number should be the encryption key used
+   on the text.  It should be in the range [0,26).  That is, the
+   number you print should obey 0 <= answer < 26.
+ - On failure, your program should print an appropriate error
+   message to stderr, then exit with EXIT_FAILURE.
+ - Provide a Makefile which compiles your program into
+   a binary called "breaker"
+Hints:
+ - Divide this problem into sub-problems.  You should probably
+   write at least two functions (other than main) to do this.
+ - Think about how you want to represent your data.  An array
+   might be handy somewhere.
+ - You may find a function you wrote in a previous classwork 
+   useful for this assignment.  Feel free to use or adapt it.
+ - Remember that everything (including characters) are numbers.
+   You might look back at the "Read encryption" assignment
+   to see an example of doing math on characters.