#include <stdio.h>


int main()
{
int year=0;
int mouth=0;
int day=0;
int sun=0;
printf("請輸入年月日");
scanf("%d %d %d",&year,&mouth,&day);
sun=(mouth-1)*30+day;
   if((year%4==0 && year%100!=0)|| year%400==0) { 
                if(mouth==1)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun); 
else if(mouth==2)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun); 
else if(mouth==3)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun); 
else if(mouth==4)
printf("%d月%d日是%d年中的%d天",mouth,day,year,+1); 
else if(mouth==5)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun); 
else if(mouth==6)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+2); 
else if(mouth==7)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+2); 
else if(mouth==8)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+3); 
else if(mouth==9)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+4); 
else if(mouth==10)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+4);
else if(mouth==11)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+5); 
else if(mouth==12)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+5); 
} 
else {
if(mouth==1)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun); 
else if(mouth==2)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun); 
else if(mouth==3)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun-1); 
else if(mouth==4)
printf("%d月%d日是%d年中的%d天",mouth,day,year); 
else if(mouth==5)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun-1); 
else if(mouth==6)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+1); 
else if(mouth==7)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+1); 
else if(mouth==8)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+2); 
else if(mouth==9)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+3); 
else if(mouth==10)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+3);
else if(mouth==11)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+4); 
else if(mouth==12)
printf("%d月%d日是%d年中的%d天",mouth,day,year,sun+4);
} 



      return 0; 

}

一開始有兩個錯誤

1.

判斷的時候寫成了if（mouth=x），所以導致輸出的結果跟出入的不一樣 應改為if（mouth==x）

2.

雖然if後面或者else if 後面都是單個語句 不用加括號，但是與第一個if對應的else後面還有一個if，不加括號的情況下系統理解為，與第一個if對應的else與這個else後面的if 組成else if

所以與第一個if對應的else後面要加大括號