C++: Mad Libs

Mad Libs is a phrasal template word game where one player prompts another for a list of words to substitute for blanks in a story, usually with funny results.

Write a program to create a Mad Libs like story. The program should read a multiline story from the input. The story will be terminated with a blank line. Then, find each replacement to be made within the story, ask the user for a word to replace it with, and make all the replacements. Stop when there are none left and print the final story.

The input should be in the form:

<name> went for a walk in the park. <he or she>
found a <noun>. <name> decided to take it home.

It should then ask for a name, a he or she and a noun (<name> gets replaced both times with the same value.)

#include <iostream>
#include <string>
using namespace std;
 
int main()
{
  string story, input;
 
  //Loop
  while(true)
  {
    //Get a line from the user
    getline(cin, input);
 
    //If it's blank, break this loop
    if(input == "\r")
      break;
 
    //Add the line to the story
    story += input;
  }
 
  //While there is a '<' in the story
  int begin;
  while((begin = story.find("<")) != string::npos)
  {
    //Get the category from between '<' and '>'
    int end = story.find(">");
    string cat = story.substr(begin + 1, end - begin - 1);
 
    //Ask the user for a replacement
    cout << "Give me a " << cat << ": ";
    cin >> input;
 
    //While there's a matching category 
    //in the story
    while((begin = story.find("<" + cat + ">")) != string::npos)
    {
      //Replace it with the user's replacement
      story.replace(begin, cat.length()+2, input);
    }
  }
 
  //Output the final story
  cout << endl << story;
 
  return 0;
}