刚开始忽略了N=1这种情况,所以WA了,
#include<iostream>
using namespace std;
int idx[] = {1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384};
int main()
{
int N, kcases = 0;
while(cin >> N && N >= 0)
{
for(int i = 0; i < 15; i++)
{
if(N <= idx[i])
{
cout << "Case " << ++kcases << ": " << i << endl;
break;
}
}
}
return 0;
}