S=1^k-2^k+3^k-...+(-1)^(k+1)*n^k? 应为 S=1^k-2^k+3^k-...+(-1)^(n+1)*n^k? 程序如下double s(int n, int k){double sum=0;int flag=-1;for(int i=1;i<=n;i++)
