根据输入的年份和月份，判断该月天数

#include"stdio.h"
void main()
{
 int a[2][3]={                          //定义数组放2月份的天数
  {29,28}
 };
 int year,month;                           //定义年、月
 printf("Please enter a year:\n");        //接受年份
 scanf("%d",&year);
 printf("Please enter a month:\n");       //接受月份
 scanf("%d",&month);
 if(1<=month<=12)                         //有效月份
 {
  if(month==1||month==3||month==5||month==7||month==8||month==10||month==12)
  {       //一年中的31天的月份
   printf("There are 31 days in the %d month of the %d\n",month,year);
  }
  else if(month==4||month==6||month==9||month==11)
  {        //一年中30天的月份
   printf("There are 30 days in the %d month of the %d\n",month,year);
  }
  else
  {
   if(year%400==0||year%4==0 && year%100!=0)
   {    //闰年的2月份
    a[0][1]=29;
    printf("There are %d days in the %d month of the %d\n",a[0][0],month,year);
   }
   else
   {   //平年的2月份
    printf("There are %d days in the %d month of the %d\n",a[0][1],month,year);
   }
  }
 }
 else
 {           //月份不在0~12的无效
  printf("输入月份无效!\n");
 }
}