STL sort sort(arr+n1, arr+n2, sortMethod() ); struct sortMethod { bool operator( const int & a1, const int & a2) { return a1 < a2; } } STL search binary_search(arr+n1, arr+n2, val, sortMethod); T* lower_bound(arr+n1, arr+n2, val, sortMethod); find from first to the last, arr[n] >= val T* upper_bound