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I always encourage novice programmers to try and use as strong warnings to GCC as possible.  At the very least, use -Wall:

 gcc -c program.c -Wall -O2

Note that GCC can only spot certain types of issues when it does extra analysis associated with the optimization flags (-O2, -O3).  This includes uninitialized variables in some situations.

If you're up to it, add:

 -W -pedantic

Spotting and fixing issues early on can save considerable time in maintenance and debugging later on.