然而题解没一个递归，我自个儿的还错了

#include<iostream>
using namespace std;
int a[31],i;
int sum(long long t,int s){ 
	if(s==i) return t; 
	else return sum(t+a[s],++s)+sum(t,++s);
}
int main(){
	while(cin>>a[i++])
	cout<<sum(0,0);
	return 0;
}

求助，半天没弄清哪里错了QAQ