C++ "Program has stopped working" - ROT-107 (Caesar cipher)

Question

I have problem with my code.
When I run this code, the correct answer appears. After a while i see an error showing that "program has stopped working" (0xC0000005). Have you got any idea why does the program not work properly? Everything seems to be ok.

#include <iostream>
#include <fstream>

using namespace std;

int k = 107;
string word;
string word_out;
fstream plik;
fstream plik_out;

int main() {
plik.open("Dane_PR2/dane_6_1.txt", ios::in);
plik_out.open("Dane_PR2/wynik_6_1.txt", ios::out);
for (int i = 0; i < 100; i++)
{
    plik >> word;
    for (int j = 0; j < word.length(); j++)
    {

        while (k>26)
        {
            k=k-26;
        }

            word_out[j] = word[j] + k;
            if (word_out[j] > 90) word_out[j] = word_out[j] - 26;

        cout << word_out[j];
        plik_out << word_out[j];
    }
    cout << endl;
    plik_out << endl;
    }
    plik.close();
    plik_out.close();
    return 0;
}

here you have input data - txt file which my program reads:

http://www74.zippyshare.com/v/4i6fg2NB/file.html

Answer 1

One major issue is that you are accessing the word_out string out-of-bounds:

word_out[j] = word[j] + k;

word_out at the time that this line is executed is empty, thus there is no index j within the string.

Change that line to:

word_out.at(j) = word[j] + k;

and you should now get an std::out_of_range exception thrown instead of a cryptic access violation error.

So you need to fix your program so that you're not going out of bounds. One possible way is to size the word_out string before you use it.

plik >> word;
word_out.resize(plik.size());