#include <iostream>
#include <string>
using namespace std;

int main () {
  string base="this is a test string.";
  string str2="n example";
  string str3="sample phrase";
  string str4="useful.";

  string str=base;                // "this is a test string."
  str.replace(9,5,str2);          // "this is an example string." (1)
  str.replace(19,6,str3,7,6);     // "this is an example phrase." (2)
  str.replace(8,10,"just a");     // "this is just a phrase."     (3)
  cout << str << endl;
}