用函数的调用来判断某年某月有多少天

#include<stdio.h>

int Printdate(int year,int month,int day)

{
if((year%4==0&&year%100!=0)||(year%400==0))  
    {  
        if(month==1||month==3||month==5||month==7||month==8||month==10||month==12)  
day=31;
        if(month==2)
day=29;
        if(month==4||month==6||month==9||month==11)
day=30;  
    }  
    else  
    {  
        if(month==1||month==3||month==5||month==7||month==8||month==10||month==12) 
day=31;  
        if(month==2) 
day=28;  
        if(month==4||month==6||month==9||month==11) 
day=30;  
    }  
switch(month)
{
case 1:
printf("January %d,该月有%d天\n",year,day);
break;
case 2:
printf("February %d,该月有%d天\n",year,day);
break;
case 3:
printf("March %d,该月有%d天\n",year,day);
break;
case 4:
printf("April %d,该月有%d天\n",year,day);
break;
case 5:
printf("May %d,该月有%d天\n",year,day);
break;
case 6:
printf("June %d,该月有%d天\n",year,day);
break;
case 7:
printf("July %d,该月有%d天\n",year,day);
break;
case 8:
printf("August %d,该月有%d天\n",year,day);
break;
case 9:
printf("September %d,该月有%d天\n",year,day);
break;
case 10:
printf("October %d,该月有%d天\n",year,day);
break;
case 11:
printf("November %d,该月有%d天\n",year,day);
break;
case 12:
printf("December %d,该月有%d天\n",year,day);
break;
default:
printf("error!\n");
return 0;
}
}
int main()
{
int month,year,day;
while(1)
{
printf("请输入年份，月份：");
scanf("%d%d",&year,&month);
Printdate(year,month,day);
}
return 0;
}