I wrote a date calculator program in Small Basic. The program ID is JQQ629.
This program calculates days between two dates. To calculate days, dates are converted to Julian days.
There are two convert subroutines DateToJD() and JDToDate(). To test these two subroutines, I wrote unit test subroutine UnitTest(). You can see the test if change "False" to "True" in line 9.