hdu4727 The Number Off of FFF

#include <stdio.h>
#define MAXN 100001

int arr[MAXN];

int main()
{
int i,n,test,index,cases=1;
scanf("%d",&test);
while(test--)
{
scanf("%d",&n);
for(i=1;i<=n;++i)
scanf("%d",&arr[i]);
index=1;
for(i=2;i<=n;++i)
{
if(arr[i]!=arr[i-1]+1)
{
index=i;
break;
}
}
printf("Case #%d: %d\n",cases++,index);
}
return 0;
}