0x03. C - Debugging

Learning objectives for this project:

0. Multiple mains
- 0-main.c: Test if function positive_or_negative() gives the correct output when given a case of 0.
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- 1-main.c: Infinite loop debugging.
2. 0 > 972?
- 2-largest_number.c: Prints largest of three integers.
3. Leap year
- 3-print_remaining_days.c: Converts a date to the day of year and determines how many days are left in the year, taking leap year into consideration.