# K & R C Programs Exercise 5-9.

K and R C, Solution to Exercise 5-9:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
C program to , Rewrite the routines of K & R C Programs Exercise 5-8 day_of_year and month_day with pointers instead of indexing.Read more about C Programming Language .

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#include <stdio.h>

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)
{
int i, leap;
char *p;

leap = (year%4 == 0 && year%100 != 0) || year%400 == 0;

/* Set `p' to point at first month in the correct row. */
p = &daytab[leap][1];

/* Move `p' along the row, to each successive month. */
for (i = 1; i < month; i++) {
day += *p;
++p;
}
return day;
}

void month_day(int year, int yearday, int *pmonth, int *pday)
{
int i, leap;
char *p;

leap = (year%4 == 0 && year%100 != 0) || year%400 == 0;
p = &daytab[leap][1];
for (i = 1; yearday > *p; i++) {
yearday -= *p;
++p;
}
*pmonth = i;
*pday = yearday;
}

int main(void)
{
int year, month, day, yearday;

year = 2012;
month = 7;
day = 9;
printf("The date is: %d-%02d-%02dn", year, month, day);
printf("day_of_year: %dn", day_of_year(year, month, day));

yearday = 61; /* 2012-03-01 */
printf("Yearday is %dn", yearday);
month_day(year, yearday, &month, &day);
printf("month_day_pointer: %d %dn", month, day);

return 0;
}

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