1 files changed, 81 insertions, 0 deletions
diff --git a/docs/html/xbc4.html b/docs/html/xbc4.html
new file mode 100755
index 0000000..a0275ed
--- /dev/null
+++ b/docs/html/xbc4.html
@@ -0,0 +1,81 @@
+<!DOCTYPE HTML PUBLIC>
+<HTML>
+<TITLE>Xbase DBMS Chapter 4</TITLE>
+<BODY BGCOLOR=#FFFFFF>
+<H1><p align="center">Date Processing</p></H1>
+<p align="center">Chapter Updated 12/09/22</p><hr>
+
+The objective of this chapter is to provide information regarding 
+the basic concepts of date arithmetic and supply generic
+C/C++ date methods.<br><br>
+
+<h2>Leap Years</h2>
+ 
+Due to the fact that it actually takes about 365 1/4 days for 
+the earth to circle the sun,  every fourth year and every fourth 
+century have an extra day added to the end of February and the year 
+is called a leap year. Leap years have 366 days, non leap years 
+have 365 days.  The following code segment describes how to
+determine if a given year is a leap year.
+
+A leap year is a year having 366 days, which can be evenly
+divisible by 4 and not by 100 or divisible by 400.
+
+There are also leap centuries.  Leap centuries are years which 
+are evenly divisible by 400.
+
+To calculate a leap year, the following code segment can be used
+
+<xmp>    
+   int year;
+        
+   if(( year % 4 == 0 && year % 100 != 0 ) || year % 400 = 0 )
+      LEAP_YEAR = TRUE;
+   else
+      LEAP_YEAR = FALSE
+</xmp>    
+                    
+
+<h2>Julian Dates</h2>
+   
+Around the time of Jesus Christ, a fellow with the name of Julias Ceasar
+established the Julian calendar.  The Julian calendar established every 
+fourth year as a leap year with 366 days and all other years having 365 days. 
+The months were set up the same as they are with a Gregorian calendar, which
+is what we use today.  A Julian date is defined as as the number of days from the
+first day of the year; February 1 would have a Julian day of 32.<br><br>
+
+From a programmer's perspective, Julian dates are useful for doing date 
+arithmetic, determining the difference between two dates or calculating
+a future or past date.<br><br>
+        
+To determine the difference between two dates,  convert both dates to a 
+Julian date and subtract one from the other.<br><br>
+
+To calculate a future or past date, convert the base date to a Julian date,
+add (or subtract) the number of days necessary to (from) it and convert the
+julian date back to a Gregorian date.<br><br>
+
+The Julian date routines use a base date of 01/01/0001. DBase julian Dates have an offset of 1721425L, reason unknown.
+<br><br>
+
+<h2>Gregorian Dates</h2>
+
+In 1582, Pope Gregor XIII introduced a corrected form of the Julian calendar.
+Every 4th year still has 366 days except for century years.  Century years
+were added as leap years if evenly divisible by 400.  The year 2000 is a leap century. 
+<br><br>
+
+The methods supplied with this software are based on gregorian dates with
+the format of CCYYMMDD for century, year, month and day.<br><br>
+
+
+<h2>Date Formats</h2>
+
+All dates are stored in the .DBF files with format CCYYMMDD.<br><br>
+All date routines work with dates formated with the same CCYYMMDD format.<br><br>
+
+<hr>
+<p><img src="xbase.jpg"><br><hr>
+</BODY>
+</HTML>