//my program's as follows
#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
    long n,m,i,j,*p,*q,count=0;
    bool found;
    cin>>n;
    p=(long *)malloc(n*4);
    for(i=0;i<n;i++)
       cin>>*(p+i);
    cin>>m;
    q=(long *)malloc(m*4);
    for(j=0;j<m;j++)
    {
        cin>>*(q+j);
        found=binary_search(p,(p+n),*(q+j));
        if(found)
           count++;
    }
    cout<<count<<endl;
    return 0;
}

Maybe, binary_search is recursive?

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int n;
vector<int> a(0);
int m;
void init_solve() {

    cin>>n;
    int c;
    for(int i=0;i<n;i++) {
        cin>>c;
        a.push_back(c);
    }

    cin>>m;
    int br=0;
    for(int i=0;i<m;i++) {
        cin>>c;
        if(binary_search(a.begin(),a.end(),c)) br++;
    }
    cout<<br<<'\n';

}

int main() {

    init_solve();

    return 0;
}

hey,friend,it's really kool,the <vector>, isn't it?:)
thanks for teaching me...