How to Subtract Days after Sorting

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C

After people are sorted in order of their birthdays, how can I subtract two birthdays to find out the days in between so that I can know if the person to the left or the right of someone has the closest birthday to them?

example:
JAN 31 ---- FEB 2 ---- FEB 15
Person1 --- Person2 --- Person3

Result: Person2 has closest birthday to person1.

In case you wonder about the leap year, February is only be counted as 28 days, unless someone has that b-day.

Should I make January = 1, like should I put
#define JANUARY 1 and do that for each month?

Then could I do something like:

if (month == JANUARY)
  dayofyear = day;
else if (month == MARCH)
  dayofyear = day+28+31;
...and so on

*C programming only.

Thanks, yeah I finally thought of something like that:

int dayOfYear = dayOfMonth + monthOffset[monthNumber];

but didn't realize about December 31 and Jan 1. People are being sorted by their birthdays, not age, so the problem says to ignore the year for that so I guess the year doesn't come into play. I guess I will just have to come up with another function or if statement for December