1 files changed, 83 insertions, 0 deletions
diff --git a/ch5/5-08_error-checking.c b/ch5/5-08_error-checking.c
new file mode 100644
index 0000000..61c15c7
--- /dev/null
+++ b/ch5/5-08_error-checking.c
@@ -0,0 +1,83 @@
+#include <stdio.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-8: There is no error checking in day_of_year or month_day.
+ * Remedy this defect.
+ *
+ */
+
+static char daytab[2][13] = {
+	{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
+	{0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
+};
+
+int day_of_year(int year, int month, int day);
+void month_day(int year, int yearday, int *pmonth, int *pday);
+
+int main() {
+	int m, d, doy;
+	m = d = 0;
+	doy = 0;
+
+	printf("Calling day_of_year(1973, 10, 32)\n> ");
+	if ((doy = day_of_year(1973, 10, 32)) > 0) {
+		printf("Oct 12nd, 1973 is day %d\n", doy);
+	} else {
+		printf("The month or day is out of range!\n");
+	}
+	printf("Calling month_day(1985, 295, ...)\n> ");
+	month_day(1985, 295, &m, &d);
+	if (m > 0 && d > 0) {
+		printf("Day 295 of year 1985 is month %d and day %d\n", m, d);
+	} else {
+		printf("month_day: day of year out of range!\n");
+	}
+	printf("Calling day_of_year(1492, 5, 14)\n> ");
+	if ((doy = day_of_year(1492, 5, 14)) > 0) {
+		printf("May 14th, 1492 is day %d\n", doy);
+	} else {
+		printf("The month or day is out of range!\n");
+	}
+	printf("Calling month_day(2012, 367, ...)\n> ");
+	month_day(2012, 367, &m, &d);
+	if (m > 0 && d > 0) {
+		printf("Day 295 of year 1985 is month %d and day %d\n", m, d);
+	} else {
+		printf("month_day: day of year out of range!\n");
+	}
+	return 0;
+}
+
+int day_of_year(int year, int month, int day) {
+	int i, leap;
+	leap = (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
+
+	if (month < 1 || month > 12) {
+		return -1;
+	}
+	if (day > daytab[leap][month] || day < 1) {
+		return -1;
+	}
+	for (i = 1; i < month; i++) {
+		day += daytab[leap][i];
+	}
+	return day;
+}
+
+void month_day(int year, int yearday, int *pmonth, int *pday) {
+	int i, leap;
+	leap = (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
+
+	// Check for edge case
+	if (yearday > 365 + leap || yearday < 1) {
+		*pmonth = 0; // Set to zero so the error is obvious
+		*pday = 0;
+		return;
+	}
+	for (i = 1; yearday > daytab[leap][i]; i++) {
+		yearday -= daytab[leap][i];
+	}
+	*pmonth = i;
+	*pday = yearday;
+}