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-rw-r--r--ch5/5-08_error-checking.c83
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
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+++ 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;
+}