判断数组内是否有几个元素之和等于m

 #include<iostream>
 using namespace std;
 int a[];
 int f(int n,int m)
 {
     if(m==||m-a[n]==)return ;
     if(n==&&m-a[n]!=)return ;
     else return f(n-,m)+f(n-,m-a[n]);
 }
 int main()
 {
     int n,m;
     cin>>n;
     for(int i=;i<=n;i++)
     {
         cin>>a[i];
     }
     cin>>m;
     if(f(n,m)==)
     cout<<"yes";
     else cout<<"no";
     return ;
 }