Versions of my so-called letter-upgrader client and server pair
whose purpose is to demonstrate the socket API
and to show the role of a protocol (first 2 versions are protocol-less, other 2 have a protocol)
the client sends a letter to the server, and the server sends another letter back,
which can be either the next or the previous letter in the alphabet
There are 4 versions:

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Hard-coded IP, port number, and letter to upgrade
client3.c - using 192.168.1.1, 9999, and R
server3.c - using 9999
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Not hard coded, user supplies IP and port number as command line arguments
client4.c - using R
server4.c
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Allows either upgrade or downgrade operation upon letter
 and institues a protocol for client to tell server which one
Hard-coded IP, port number, and letter to upgrade
 letter to upgrade (using R), and operation (using upgrade)
client3-with-protocol.c - using 192.168.1.1, 9999, R, and upgrade
server3-with-protocol.c - using 9999
--------------------
Allows either upgrade or downgrade operation upon letter
 and institues a protocol for client to tell server which one
Not hard coded, user supplies IP, port number, letter, and operation as command line arguments
client4-with-protocol.c
server4-with-protocol.c
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