Question

I wrote the code below that successfully gets a random line from a file; however, I need to be able to modify one of the lines, so I need to be able to get the line character by character.
How can I change my code to do this?

Answer 1

Use std::istream::get instead of std::getline. Just read your string character by character until you reach \n, EOF or other errors. I also recommend you read the full std::istream reference.

Good luck with your homework!

UPDATE:

OK, I don’t think an example will hurt. Here is how I’d do it if I were you:

#include <string>
#include <iostream>
#include <fstream>
#include <cstdlib>

using namespace std;

static std::string
answer (const string & question)
{
    std::string answer;
    const string filename = "answerfile.txt";
    ifstream file (filename.c_str ());

    if (!file)
    {
        cerr << "Can't open '" << filename << "' file.\n";
        exit (1);
    } 

    for (int i = 0, r = rand () % 5; i <= r; ++i)
    {
        answer.clear ();
        char c;

        while (file.get (c).good () && c != '\n')
        {
            if (c == 'i') c = 'I'; // Replace character? :)
            answer.append (1, c);
        }
    }

    return answer;
}

int
main ()
{
    srand (time (NULL));

    string question;

    cout << "Please enter a question: " << flush;
    cin >> question;
    cout << answer (question) << endl;
}

… the only thing is that I have no idea why do you need to read string char by char in order to modify it. You can modify std::string object, which is even easier. Let’s say you want to replace “I think” with “what if”? You might be better off reading more about
std::string and using find, erase, replace etc.

UPDATE 2:

What happens with your latest code is simply this – you open a file, then you get its content character by character until you reach newline (\n). So in either case you will end up reading the first line and then your do-while loop will terminate. If you look into my example, I did while loop that reads line until \n inside a for loop. So that is basically what you should do – repeat your do-while loop for as many times as many lines you want/can get from that file. For example, something like this will read you two lines:

for (int i = 1; i <= 2; ++i)
{
    do
    {  

        answerfile.get (answer);
        cout << answer << " (from line " << i << ")\n";
    }
    while (answer != '\n');
}