C语言小程序如何判断两个日期之差

#include<stdio.h>
intleapyear(intyear)
{
 if((year%4==0&&year%100!=0)||year%400==0)
  return1;
 else
  return0;
}
intdays(int*day1,int*day2)
{
 inti=0;
 int*tmp;
 intdiff=0;
 constintmonth[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
 if(day1[0]==day2[0])
 {
  if(day1[1]==day2[1])
  {
   diff=day1[2]-day2[2];
   diff=(diff<0)?(-diff):diff;
  }
  else
  {
   if(day1[1]<day2[1])    //day1=1991-5-8  day2=1991-6-2
   {
    tmp=day1;      //day1=1991-6-2  day2=1991-5-8
    day1=day2;
    day2=tmp;
   }
   for(i=day2[1]+1;i<day1[1];i++)
   {
    diff+= month[i];
   }
   diff+=month[day2[1]]-day2[2]+day1[2];
   if(day2[1]<=2&&day1[1]>2)
    if(leapyear(day2[0]))
     diff++;
  }
 }
 else
 {
  if(day1[0]<day2[0])
  {
   tmp=day1; 
   day1=day2;
   day2=tmp;
  }
  for(i=day2[0]+1;i<day1[0];i++)
  {
   if(leapyear(i))
    diff+=366;
   else
    diff+=365;
  }
  for(i=day2[1]+1;i<=12;i++)     //day1=1992-1-1  day2=1991-1-1
  {
   diff+=month[i];
  }
  diff+=(month[day2[1]]-day2[2]);
  if(day2[1]<=2)
   if(leapyear(day2[0]))
    diff++;
  for(i=1;i<day1[1];i++)
  {
   diff+=month[i];
  }
  diff+=day1[2];
  if(day1[1]>2)
   if(leapyear(day1[0]))
    diff++;
 }
 returndiff;
}
intmain()
{
 intday1[3],day2[3];
 intday=0;
 printf("输入日期：");
 scanf("%d-%d-%d",&day1[0],&day1[1],&day1[2]);
 printf("输入另一个日期：");
 scanf("%d-%d-%d",&day2[0],&day2[1],&day2[2]);
 day=days(day1,day2);
 printf("两个日期之间共有%d天。\n",day);
 return0;
}