Write a C program with a focus on system calls. So only use read() and write() for obtaining input and creating output - do not use printf, cout, sprintf or similar functions.

The program should continually take characters from STDIN and should terminate with a Control-D.

This program reads characters from STDIN, converts them if a "-U" argument is passed to the program (example: "./program -U"), and writes the characters to STDOUT. The character stream may contain any ASCII value.

If a "-U" flag is present take all alphabetic characters and output all to STDOUT in uppercase.

If no flag is present you can just exit.

NOTE: Must use read() and write() system calls.