Makefile for Linux from Xcode-written C++ program

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http://stackoverflow.com – I've written a simple c++ program on Xcode, all contained within ONE FILE called huffmanGenerator.cpp. The program reads input from a file on the user's computer, and writes output to a file saved to their computer. The instructor has asked us to create a makefile so that our programs compile and run with g++ OR gcc in Linux; however she never showed us how to do so, and when the class asked for help, her answer was we could figure it out. I found many links online, but they're all very confusing as this is all new to me, and most of them fail to answer even the most basic questions like w (HowTos)