I Wonder why I have to sort in advance the elements in the array of the teacher in order to use binary_search otherwise I get WA

I have use STL and had WA1 too. But I use count(). Here is my code in C++
#pragma comment(linker, "/STACK:16777216")
#include <iostream>
#include <algorithm>
using namespace std;
 void main()
 {
  int  v[15000],s[1000000],z=0,i,j,n,st;
  cin>>n;
  for (i = 0; i <=n-1; i++) cin>>v[i];
  cin>>st;
  for (i = 0; i <=st-1; i++) cin>>s[i];

  for (i = 0; i <=st-1; i++)
  z+=count(s,s+st,v[i]);
  cout<<z;
  }
 what's wrong?

I use binary search and now I have WA2 :) Help me please!

#include <iostream>
#include <algorithm>
using namespace std;
void main()
{
int v[15000],s,z=0,i,j,n,st,t;
cin>>n;
for (i = 0; i <=n-1; i++) {cin>>t;if (t!=v[i-1]) v[i]=t; }

cin>>st;
for (i = 0; i <=st-1; i++) {cin>>s;
if(binary_search(v,v+n,s)==true)z++;          }
cout<<z;
}

Edited by author 18.02.2007 03:01