Binary Search

 1 template <typename T>
 2 int binarySearch(<const vector<T> & a, const T &x) 
 3 {
 4     int low=0,high=a.size()-1;
 5 
 6     while(low<=high)
 7     {   
 8         int mid=(low+high)/2;
 9         if (a[mid]<x)
10             low=mid+1;
11         else if (a[mid]>x)
12             high = mid-1;
13         else return mid;
14     }   
15     return -1; 
16 }