5.9

1 files changed, 63 insertions, 0 deletions

diff --git a/5.9.c b/5.9.c
new file mode 100644
index 0000000..e768bd5
--- /dev/null
+++ b/5.9.c
@@ -0,0 +1,63 @@
+#include <stdio.h>
+
+#define LEAP_YEAR_DAYS 366
+#define NON_LEAP_YEAR_DAYS 365
+#define NO_OF_MONTHS 12
+
+int year_day(int day, int month, int year);
+void month_day(int *day, int *month, int year, int year_day_val);
+
+int 
+main(void)
+{
+  int day, month, year, year_day_val;
+
+  year = 2020;
+  printf("yd: %d\n", (year_day_val = year_day(15, 2, year)));
+
+  month_day(&day, &month, year, year_day_val);
+  printf("md: %d-%d\n", day, month);
+}
+
+static char daytab[][12] = {
+  {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
+  {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
+};
+
+int 
+year_day(int day, int month, int year)
+{
+  int i, leap;
+
+  leap = ((!year%4 && year%100 ) || !year%400);
+
+  if (month > NO_OF_MONTHS || day > *(*(daytab+leap)+month-1))
+    return -1;
+
+  for (i = 0, --month; i < month; i++)
+    day += *(*(daytab+leap)+i);
+
+  return day;
+}
+
+void
+month_day(int *day, int *month, int year, int year_day_val)
+{
+  int i, leap;
+
+  leap = ((!year%4 && year%100 ) || !year%400);
+
+  if ((leap && year_day_val > LEAP_YEAR_DAYS) || (!leap && year_day_val > NON_LEAP_YEAR_DAYS)) {
+    *month = -1;
+    *day = -1;
+    return;
+  } 
+
+  for (i = 1; year_day_val > *(*(daytab+leap)+i-1); i++)
+    year_day_val -= *(*(daytab+leap)+i-1);
+
+  *month = i;
+  *day = year_day_val;
+
+  return;
+}