求解while怎么用

#include<stdio.h>
main()
{
int year, month;
printf("请输入年份:");
scanf("%d",&year);
printf("请输入月份:");
scanf("%d",&month);
switch(month)
{
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
printf("%d年%d月是31天",year,month);
break;
case 4:
case 6:
case 9:
case 11:
printf("%d年%d月是30天",year,month);
break;
case 2:
{
if(year%4==0&&year%100!=0||year%400==0)
printf("%d年%d月份有29天",year,month);
else
printf("%d年%d月份有28天",year,month);
break;
}
}
}
在这里面塞个while句子 ，判定月份是1到12之间的
脑袋想疼了 也不知道往那里塞