求集合的子集

#include <iostream>
#include<string>
using namespace std;
void  trail(string[],int[],int,int);
int main()
{
int n,k=0;
cout<<"Please enter the number of the element :";
cin>>n;
string a[100];
int b[100]={0};
for (int i=0;i<n;i++)
{
cout<<"Please enter NO."<<i+1<<" element :";
cin>>a[i];
}
cout<<"All of the subset is:"<<endl;
trail(a,b,0,n);
return 0;
}
void trail(string a[],int b[],int k,int n)
{
int j;
if (k<n)
{
trail(a,b,k+1,n);
b[k]=1-b[k];
trail(a,b,k+1,n);
}
else
{
cout<<"{";
for (j=0;j<=n;j++)
{
if (b[j])
{
cout<<a[j]<<" ";
}
}
cout<<"} ";
}

}