Exercise 5.9. Rewrite the routines day_of_year and month_day with pointers instead of indexing.Exercise 5.9. Rewrite the routines day_of_year and month_day with pointers instead of indexing.

Exercise 5.9. Rewrite the routines day_of_year and month_day with pointers instead of indexing.

/* day_of_year */

int day_of_year(int year, int month, int day)

{

    int leap;

    char *p;

    

    if(year < 1)

        return -1;

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

    p = daytab[leap];

    if(month < 1 || month > 12)

        return -1;

    if(day < 1 || day > *(p + month))

        return -1;

    while(month > 0)

    {

        day += *p++;

        month--;

    }

    return day;

}

/* month_day */

void month_day(int year, int yearday, int *pmonth, int *pday)

{

    int leap;

    char *p;

    char *tmp;

    

    if(year < 1 || yearday < 1)

    {

        *pmonth = -1;

        *pday = -1;

        return;

    }

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

    p = daytab[leap];

    tmp = p;

    if(leap == 1 && yearday > 366)

    {

        *pmonth = -1;

        *pday = -1;

        return;

    }

    if(leap == 0 && yearday > 365)

    {

        *pmonth = -1;

        *pday = -1;

        return;

    }  

    while(yearday > *p++)

    {

        yearday -= *p;

    }

    *pmonth = p - tmp;

    *pday = yearday;

}