我正在编写一个程序，它输出用户输入的最早日期，但出现了一些问题

Question

I am writing this program which prompt the user to enter a any number of dates and output the earliest when the user enter 0/0/0. But my program outputs the result after I input the first 2 dates. And when I enter more dates, it keeps comparing them but at the end, it gives a wrong result. Please help me fix it. Here is my code

/*
//Input
Enter a date (mm/dd/yy): 3/6/08
Enter a date (mm/dd/yy): 5/17/07
Enter a date (mm/dd/yy): 6/3/07
Enter a date (mm/dd/yy): 0/0/0
//output
5/17/07 is the earliest date*/


#include <stdio.h>
#include <stdlib.h>

int main(int argc, char const *argv[])
{
int month, day, year;
int month2, day2, year2;
printf("Enter a date (mm/dd/yy): ");
scanf("%d/%d/%d", &month2, &day2, &year2);

while(month != 0 && day != 0 && year != 0)
{
    printf("Enter a date (mm/dd/yy): ");
    scanf("%d/%d/%d", &month, &day, &year);


    if(year == year2)
    {
        if(month == month2)
        {
            if(day > day2)
            {
                printf("%d/%d/%d is the earliest date\n", month2, day2, year2);
            }
            else
            {
                printf("%d/%d/%d is the earliest date\n",month, day, year);
            }
        }
        else if (month > month2)
        {
            printf("%d/%d/%d is the earliest date\n", month2, day2, year2);
        }
        else
        {
            printf("%d/%d/%d is the earliest date\n",month, day, year);
        }

    }
    else if(year > year2)
    {
        printf("%d/%d/%d is the earliest date\n", month2, day2, year2);
    }
    else
    {
        printf("%d/%d/%d is the earliest date\n",month, day, year);
    }


} 
return 0;
}

Answer 1

The first time year, moth, day are used, they lack initialization.

// int month, day, year;
int month = -1;
int day = 0;
int year = 0;
// ...
while(month != 0 && day != 0 && year != 0)

Otherwise OP is close, yet needs to change the earliest date as various new dates occur. @Barmar . Print the earliest date once, after the loop.

The loop exit condition test needs to occur right after data input.

while (1) {
  printf("Enter a date (mm/dd/yy): ");
  scanf("%d/%d/%d", &month, &day, &year);
  printf("%d/%d/%d is the date entered\n", month, day, year);
  if (!(month != 0 && day != 0 && year != 0)) {
    break;
  }

  int earlier = 0;
  if (year < year2) {
    earlier = 1;
  } else if (year == year2) {
    if (month < month2) {
      earlier = 1;
    } else if (month == month2) {
      if (day < day2) {
        earlier = 1;
      }
    }
  }
  if (earlier) {
    year2 = year; 
    month2 = month; 
    day2 = day;
  }
}

printf("%d/%d/%d is the earliest date\n", month2, day2, year2);

---

Other improvements include:

Reading a line of input and then parsing for a date.

Checking for scan errors.

Flush the output to insure the prompt occurs before input.

printf("Enter a date (mm/dd/yy): ");
fflush(stdout);

Using better names.. Rather than year2 , perhaps early_year ?

A do loop rather than while one as the loop iterates at least once. Also then month, day, year can move to the inside of the loop.

Range checking for valid dates ...