You can think of an iterator as a pointer to elements of a container. All STL (Standard Template Library) containers provide the basic iterator type along with its const counterpart. The const iterator of a container should be used when the elements accessed through it are not supposed to be modified, like in the following example:

 void main() {	string s ("hello world"); // s contains 11 characters 	string::const_iterator p = s.begin(); //p is a const iterator pointing to the first element of s 	size_t n = 0; 	while ( p < s.end() ) {   // a loop that count the number of chars in s	 n++;    p++;   // move to the next element of s	}	cout<