结构体\判断日期是否合法（代码分步解析）

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
 
//检查日期函数_声明
int checkDate(Date date);
 
int main()
{
  int check=0;
  Date date;
 
  do
  {
    printf("请输入一个日期(格式为YYYY-MM-DD):\n");
    printf("位数不足不补零#\n");
    scanf("%d-%d-%d",&date.year ,&date.month,&date.day);
    check=checkDate(date);
  }while(check!=1);
  printf("日期正确！\n");
 
  system("pause");
  return 0;
}

typedef struct Date
{
  int year;
  int month;
  int day;
}Date;

//检查日期函数_定义
int checkDate(Date date)
{
  int check=0;
  
  //年份判断
  if(date.year<1900 || date.year>2100)
  {
    printf("年份错误！\n");
    return check;
  }
 
  //月份判断
  if(date.month<1 || date.month>12)
  {
    printf("月份错误！\n");
    return check;
  }
 
  int a=date.year;
  int m=date.month;
  //若为闰年，28天
  if ((a%4==0 && a%100!=0) || (a%400==0))
  {
    if(date.month==2 && date.day<=28 && date.day>=1)
    {
      printf("闰年日期错误！\n");
      return check;
    }
  }
  int judge=-1;
  //普通日期判断(1-31 0-30 -1-29)
  switch(m)
  {
  case 1:
    judge=1;
    break;
  case 2:
    judge=-1;
    break;
  case 3:
    judge=1;
    break;
  case 4:
    judge=0;
    break;
  case 5:
    judge=1;
    break;
  case 6:
    judge=0;
    break;
  case 7:
    judge=1;
    break;
  case 8:
    judge=1;
    break;
  case 9:
    judge=0;
    break;
  case 10:
    judge=1;
    break;
  case 11:
    judge=0;
    break;
  case 12:
    judge=1;
    break;
  }
  if((judge==1 && (date.day>31 || date.day<1)) || (judge==0 && (date.day>30 || date.day<1)) || (judge==-1 && (date.day>29 || date.day<1)))
  {
    printf("日期错误！\n");
    return check;
  }
 
  check=1;
  return check;
}