C++ Go back a line

I'm writing a multiple lines system, like this:

string readLines(string x)
{
    string line = "a";
    string result;

    while (1)
    {
        cout << x;
        getline(cin, line)

        if(line != "")
            result = result + "\n" + line;
        else
            break;
    }
    return result;
}

Is working fine, but I want be able to edit the previous line, for example, I'm typing something like this:

Helo,
World

I want to back on helo and fix my typo. How can I do this?