binary_search

// binary_search example#include <iostream>#include <algorithm>#include <vector>using namespace std;bool myfunction (int i,int j){     return (i<j);}int main () {  int myints[] = {1,2,3,4,5,4,3,2,1};  vector<int> v(myints, myints+9);   // 1 2 3 4 5 4 3 2 1  // using default comparison:  sort (v.begin(), v.end());    cout << "looking for a 3... ";  if (binary_search(v.begin(), v.end(), 3)){    cout << "found!\n";  }  else {    cout << "not found.\n";  }  // using myfunction as comp:  sort (v.begin(), v.end(), myfunction);  cout << "looking for a 6... ";  if (binary_search (v.begin(), v.end(), 6, myfunction)){    cout << "found!\n";  }  else {      cout << "not found.\n";  }  return 0;}