c语言：输入一个日期，求输入日期三天后的日期

int a;
scanf（"%d",&i）;
i=i 3;
printf（"三天后的日期为:%d",i）;

#include
#include
int main() //
{
struct tm a;
char b[128];
time_t c;
int y,m,d;
printf("Enter date eg:2013-03-29\n");
scanf("%d-%d-%d",&y,&m,&d);
a.tm_year=y-1900;
a.tm_mon=m-1;
a.tm_mday=d;
a.tm_hour=12;
a.tm_min=1;
a.tm_sec=1;
a.tm_isdst=0;
c=mktime(&a);
c=c+86400+86400+86400;
a=*gmtime(&c);
strftime( b, 128, "Tow days later is %x .\n", &a);
printf(b);
getchar();
return 0;
}

#include "stdio.h"
int main()
{int y,m,d,mon[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
scanf("%d%d%d",&y,&m,&d);
d+=3;
if(y%4==0&&y%100||y%400==0)mon[2]++;
if(d>mon[m]){d-=mon[m];m++;}
if(m>12){m=1;y++;}
printf("%d-%d-%d\n",y,m,d);
return 0;
}

#include
//包含此文件是要用到MessageBeep（0）这个函数在输入错误时发出声音提示，若不需要可将这个头文件和MessageBeep（0）删掉
#include
using namespace std;
//定义日期类
class Cdate
{ int year,month,day;
public:
Cdate(int x=1,int y=1, int z=1):year(x),month(y),day(z){}//带默认值的构造函数
~Cdate(){}
void SetDate();
void AddDate();
void ShowDate();
};
//设置日期函数
void Cdate::SetDate()
{cout<<"请按日月年的格式输入日期："<cin>>day>>month>>year;
start:
if(month<1||month>12)
{MessageBeep(0 );
cout<<"输入错误！请按日月年的格式重新输入日期："<cin>>day>>month>>year;goto start;}
if(day<1||day>31)
{MessageBeep(0 );
cout<<"输入错误！请按日月年的格式重新输入日期："<cin>>day>>month>>year;goto start;}
if (month==2)
if(year%4==0&&year%100!=0||year%400==0)
{if(day>29&&day<32)
{MessageBeep(0 );
cout<<"输入错误！请按日月年的格式重新输入日期："<cin>>day>>month>>year;goto start;}
}
else
{if(day>28&&day<32)
{MessageBeep(0 );
cout<<"输入错误！请按日月年的格式重新输入日期："<cin>>day>>month>>year;goto start;}
}
}

//日期加三函数
void Cdate::AddDate()
{
switch(month)
{case 1:if (day<=28)
day+=3;
else {month+=1;day=day+3-31;}
break;
case 2: if(year%4==0&&year%100!=0||year%400==0)
{
if (day<=26)
day+=3;
else {month+=1;day=day+3-29;}
}
else
{
if (day<=25)
day+=3;
else {month+=1;day=day+3-28;}
}
break;
case 3:if (day<=28)
day+=3;
else {month+=1;day=day+3-31;}
break;
case 4:if (day<=27)
day+=3;
else {month+=1;day=day+3-30;}
break;
case 5:if (day<=28)
day+=3;
else {month+=1;day=day+3-31;}
break;
case 6:if (day<=27)
day+=3;
else {month+=1;day=day+3-30;}
break;
case 7:if (day<=28)
day+=3;
else {month+=1;day=day+3-31;}
case 8:if (day<=28)
day+=3;
else {month+=1;day=day+3-31;}
break;
case 9:if (day<=27)
day+=3;
else {month+=1;day=day+3-30;}
break;
case 10:if (day<=28)
day+=3;
else {month+=1;day=day+3-31;}
break;
case 11:if (day<=27)
day+=3;
else {month+=1;day=day+3-30;}
break;
case 12:if (day<=28)
day+=3;
else {year+=1;month=1;day=day+3-31;}
break;
}
}
//显示日期函数
void Cdate::ShowDate()
{
cout<<"日期为："<cout<}
int main()
{
Cdate d;
d.SetDate();
d.AddDate();
d.ShowDate();
return 0;
}