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#include <stdio.h>
/* The C Programming Language: 2nd Edition
*
* Exercise 5-9: Rewrite the routines day_of_year() and month_day() with
* pointers instead of indexing.
*/
static char daytab[] = {
0, 31, 28, 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 i, m, d, doy;
int tvals[][4] = {
{ 2012, 2, 29, 60 },
{ 2013, 3, 1, 60 },
{ 1985, 10, 22, 295 }
};
m = d = 0;
doy = 0;
// It said nothing about avoiding indexing in main()!
for (i = 0; i < 3; i++) {
doy = day_of_year(tvals[i][0], tvals[i][1], tvals[i][2]);
month_day(tvals[i][0], doy, &m, &d);
if (doy > 0 && m != 0 && d != 0) {
printf("%4d-%02d-%02d is day %3d of the year. ", tvals[i][0], tvals[i][1], tvals[i][2], doy);
printf("Day %3d of %4d is month %2d and day %3d.\n", doy, tvals[i][0], m, d);
} else {
printf("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;
}
// Slightly complicated pointer math is needed to account for leap years
if (day > *(daytab + month) + ((month == 2) ? leap : 0) || day < 1) {
return -1;
}
for (i = 1; i < month; i++) {
// here, too
day += *(daytab + i) + ((i ==2) ? leap : 0);
}
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;
if (yearday > 365 + leap || yearday < 1) {
*pmonth = 0;
*pday = 0;
return;
}
// ...and here. :P
for (i = 1; yearday > *(daytab + i) + ((i == 2) ? leap : 0); i++) {
yearday -= *(daytab + i) + ((i == 2) ? leap : 0);
}
*pmonth = i;
*pday = yearday;
}
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