为什么这道题会WA

#include
#include
#include
#include

int main()
{
int N=0,i=0,j=0,pa,pb;
int index =0;
double sum=10;
char oper = '+';
double * res;
scanf("%d\n",&N);
res = (double *)malloc(N*8);

for(i=0;i {
scanf("%d %c %d",&pa,&oper,&pb);
switch(oper)
{
case '+':res[i]=abs((pa + pb)-9); index = (sum > res[i])? i:index;
sum = (sum > res[i])?res[i]:sum;
case '-':res[i]=abs((pa - pb)-9); index = (sum > res[i])? i:index;
sum = (sum > res[i])?res[i]:sum;
case '*':res[i]=abs((pa * pb)-9); index = (sum > res[i])? i:index;
sum = (sum > res[i])?res[i]:sum;
case '/':res[i]=fabs((pa*1.0 / pb)-9); index = (sum > res[i])? i:index;
sum = (sum > res[i])?res[i]:sum;
}

}
printf("%d\n",index+1);

return 0;
}

//刚做完，仅供参考