C++ string find() Search sub string

#include <iostream>
#include <string>
using namespace std;
int main()//from w w  w . jav  a 2  s .co m
{
   string string1 = "this is a test";
   string s1, s2, s3;
   int j, k;
   cout << "The original string is " << string1 << endl;
   j = int(string1.find('I'));
   cout << "  The first position of an 'I' is " << j << endl;
   k = int(string1.find('I', (j+1)));
   cout << "  The next position of an 'I' is " << k << endl;
   j = int(string1.find("THEORY"));
   cout << "  The first location of \"THEORY\" is " << j << endl;
   k = int(string1.find("ING"));
   cout << "  The first index of \"ING\" is " << k << endl;
   // Now extract three substrings
   s1 = string1.substr(2,5);
   s2 = string1.substr(19,3);
   s3 = string1.substr(6,8);
   cout  << "The substrings extracted are:" << endl << "  " << s1 + s2 + s3 << endl;
   return 0;
}