Censor Input - Find/Replace each word of given length

/** censor input (generic challenge question)
 *  replaces all words that are the same length as the replacement string
 *  provided as argv[1] (default "****") outputting each line with an
 *  intervening newline (blank line).
 */
#include <iostream>
#include <sstream>
#include <string>

int main (int argc, char **argv) {

    std::string line;   /* string to hold each line */
    const std::string repl = argc > 1 ? argv[1] : "****";   /* replacement */

    while (getline (std::cin, line)) {      /* read each line */
        std::string word;                   /* string to hold each word */
        std::stringstream s (line);         /* stringstream to parse line */
        while (s >> word)                   /* read each word */
            if (word.length() == repl.length()) /* lengths equal, replace */
                line.replace (line.find (word, 0), repl.length(), repl);
        std::cout << line << "\n\n";        /* output newlines */
    }
}

/*

**Example Input**

    $ cat ../dat/captnjack.txt
    This is a tale
    Of Captain Jack Sparrow
    A Pirate So Brave
    On the Seven Seas.


**Example Use/Output**

    $ ./getline_repl < ../dat/captnjack.txt
    **** is a ****

    Of Captain **** Sparrow

    A Pirate So Brave

    On the Seven Seas.


  Specifying the replacement as the 1st program argument

    $ ./getline_repl +++++ < ../dat/captnjack.txt
    This is a tale

    Of Captain Jack Sparrow

    A Pirate So +++++

    On the +++++ +++++


*/