/*
  Name:    ex6-10.c
  Purpose: Find the earliest date in a sequence of dates
  Author:  Bill Slough

  Notes:   datecmp is identical to the function we used for ex5-9
           dates are processed using a "loop and a half"
           user is expected to enter 0/0/0 to terminate input
*/

#include <stdio.h>
#define TRUE 1

int datecmp(int thisMonth, int thisDay, int thisYear,
            int thatMonth, int thatDay, int thatYear);

int main() {
    int earliestMonth = 12;
    int earliestDay = 31;
    int earliestYear = 99;    /* "infinity" date */
    
    int month, day, year;     /* next date to process */
    int count = 0;            /* number of dates processed */

    while (TRUE) {
        /* get the next date */
        printf("Enter a date (mm/dd/yy): ");
        scanf("%d/%d/%d", &month, &day, &year);

        /* terminate loop if this is the sentinel date */
        if (month == 0 && day == 0 && year == 0)
            break;

        /* process this date */
        count++;
        if (datecmp(month, day, year,
                    earliestMonth, earliestDay, earliestYear) == -1) {
            /* this date is the earliest seen so far */
            earliestMonth = month;
            earliestDay = day;
            earliestYear = year;
        }
    }
    /* Display the result */
    if (count == 0)
        printf("No dates were entered!\n");
    else
        printf("%d/%d/%2.2d is the earliest date\n",
               earliestMonth, earliestDay, earliestYear);
    
    return 0;
}

int datecmp(int thisMonth, int thisDay, int thisYear,
            int thatMonth, int thatDay, int thatYear) {
    /* Compare two dates:

       Given:  thisMonth/thisDay/thisYear vs. thatMonth/thatDay/thatYear

       Result: -1 if this date < that date
                0 if this date = that date
               +1 if this date > that date
    */

    /* Nothing is known about the dates yet */
    if (thisYear < thatYear)
        return -1;
    else if (thisYear > thatYear)
        return +1;

    /* Dates are in the same year */
    if (thisMonth < thatMonth)
        return -1;
    else if (thisMonth > thatMonth)
        return +1;

    /* Dates are in the same year and month */
    if (thisDay < thatDay)
        return -1;
    else if (thisDay == thatDay)
        return 0;
    else
        return +1;
}