C++ operator[]

boolean operator [] (int pos);
reference operator[] (int pos); 

#include <iostream>
#include <bitset>
using namespace std;
int main()
{
bitset<4> b;
b[1]=1;
b[2]=b[1];
cout<< "b :" << b;
return 0;
} 

b :0110 

#include <iostream>
#include <bitset>
using namespace std;
int main()
{
bitset<4> b(string("1001"));
b[1]=1;
b[2]=b[1];
cout<< "b :" << b;
return 0;
} 

b :1111