First you have a serial number which was converted from a date, for example : 40988 would be March 21st 2012. How could I then return 21 knowing that the serial number is 40988 and by NOT using the date object? I also have 2 other functions that I can use : numberOfDaysYear(year) which returns the number of days for a specific year (365 or 366) and I also have numberOfDaysMonth(month, year) which returns the number of days for a specific month and a specific year (31, 30, 28 or 29). The year limit goes from 1900 all the way to 2199, so this is what I started with

`

  //Count the number of 365 years and 366 years

  var counterNormalYears = 0
  var counterLeapYears = 0

  for (let i = 1900; i <= 2199; i  ) {
     if (numberOfDaysYear(i) == 365) {
        counterNormalYears  = 1
     }
     else if (numberOfDaysYear(i) == 366) {
        counterLeapYears  = 1
     }
  } 

` Moving on from here what kind of approach could I take to then find the days that the date has without using the date object?

CodePudding user response：

I'd probably do it like

let day = 40988, year = 1899, month = 0;
while (day >= 0) day -= numberOfDaysYear(  year);
day  = numberOfDaysYear(year);
while (day >= 0) day -= numberOfDaysMonth(  month, year);
day  = numberOfDaysMonth(month, year);

To explain ...

1. start at 1899, because I use pre-increment for obvious reasons
2. first thing that happens is the number of days in 1970 (using YOUR function) is subtracted from days ... since I use pre-increment, 1970 is passed in on the first loop
3. since we've gone below zero, add that last number of days in the last used year back to days
4. similar algorithm for month - subtract from days until below zero
5. similar backtrack for month as in step 3
6. you may need to adjust day by 2 - because of maths