Binary search in c++

#include <iostream>
using namespace std;

int binarysearch(int a[], int n, int key)

{

int s=0, e=n;

while(s<=e)
{
  
 int mid = (s+e)/2;
  
  if(a[mid]==key)
  return mid;
  
  else if(key<mid)
  e=mid-1;
  
  else
  s=mid+1;
  
}

return -1;
  

}

int main()
{
int n;
cin>>n;

int a[n],i,key;

for(i=0; i<n; i++)
cin>>a[i];

cin>>key;

cout << binarysearch(a,n,key);

return 0;

}