新人求解两个程序为什么输出不同？

#include
int main()
{
int year,month,day,days2=0,days=0,days101=0;
scanf("%d %d %d",&year,&month,&day);
if(((year%4==0)&&year%100!=0)||(year%400==0))
days2=29;
else
days2=28;
switch(month - 1)
{
case 12:
days=days+31;
case 11:
days=days+30;
case 10:
days=days+31;
case 9:
days=days+30;
case 8:
days=days+31;
case 7:
days=days+31;
case 6:
days=days+30;
case 5:
days=days+31;
case 4:
days=days+30;
case 3:
days=days+31;
case 2:
days=days+days2;
case 1:
days=days+31;
}
days101=31+days2+31+30+31+30+31+31+30+1;
days=days+day;
if(days printf("%d days shy",days101-days);
else if(days>=days101)
printf("over %d days",days-days101);
return 0;
}

#include
int main()
{
int year,month,day,days=0,days2=0,days101=0;
scanf("%d %d %d",&year,&month,&day);
if((year%4==0&&year%100!=0)||(year%400==0))
{
days2=29;
}
else
{
days2=28;
}
switch(month-1)
{
case12:
days=days+31;
case11:
days=days+30;
case10:
days=days+31;
case9:
days=days+30;
case8:
days=days+31;
case7:
days=days+31;
case6:
days=days+30;
case5:
days=days+31;
case4:
days=days+30;
case3:
days=days+31;
case2:
days=days+days2;
case1:
days=days+31;
}
days=days+day;
days101=31+days2+31+30+31+30+31+31+30+1;
if(days>=days101)
{
printf("over %d days",days-days101);
}
else
{
printf("%d days shy",days101-days);
}
return 0;
}

两个程序都有问题，第一个根本没法编译

 #include "stdio.h"

int main()
{
int year,month,day,days2=0,days=0,days101=0;
scanf("%d %d %d",&year,&month,&day);
if(((year%4==0)&&year%100!=0)||(year%400==0))
days2=29;
else
days2=28;
switch(month - 1)
{
case 12:
days=days+31;
case 11:
days=days+30;
case 10:
days=days+31;
case 9:
days=days+30;
case 8:
days=days+31;
case 7:
days=days+31;
case 6:
days=days+30;
case 5:
days=days+31;
case 4:
days=days+30;
case 3:
days=days+31;
case 2:
days=days+days2;
case 1:
days=days+31;
}
days101=31+days2+31+30+31+30+31+31+30+1;
days=days+day;
if(days<days101) printf("%d days shy",days101-days); //修改这里
else if(days>=days101)
printf("over %d days",days-days101);
return 0;
}

第二个程序

#include "stdio.h"

int main()
{
int year,month,day,days=0,days2=0,days101=0;
scanf("%d %d %d",&year,&month,&day);
if((year%4==0&&year%100!=0)||(year%400==0))
{
days2=29;
}
else
{
days2=28;
}
switch(month-1)
{
case 12: //这里和以下都缺少空格
days=days+31;
case 11:
days=days+30;
case 10:
days=days+31;
case 9:
days=days+30;
case 8:
days=days+31;
case 7:
days=days+31;
case 6:
days=days+30;
case 5:
days=days+31;
case 4:
days=days+30;
case 3:
days=days+31;
case 2:
days=days+days2;
case 1:
days=days+31;
}
days=days+day;
days101=31+days2+31+30+31+30+31+31+30+1;
if(days>=days101)
{
printf("over %d days",days-days101);
}
else
{
printf("%d days shy",days101-days);
}
return 0;
}

因为你没有说你的程序打算干嘛，以上讨论仅仅是综合两个错误的程序给出的最可能的正确的版本。如果还有问题请追问。
如果问题解决，请点我回答右边的采纳。

希望你学会提问，回答你这种描述不清的问题特别艰难。