Writing to a file with fstream and cstring - c++

Question

#include <fstream>
#include <iostream>
#include <cstring>
using namespace std;
int main()
{
char filename[20] = "filename";
char userInput;
ofstream myFile;
cout << "Enter filename: ";
cin.getline(filename, sizeof(filename));
myFile.open(filename);
if(myFile.fail())
{
cout << "Error opening file: "
<< filename << "\n";
return 1;
}
cout << "Add text to the file: ";
cin.get(userInput);
while(cin.good() && userInput)
{
myFile.put(userInput);
cin.get(userInput);
}
myFile.close();
return 0;
}
Im having trouble terminating the input without force quiting it(It still writes to the file).
This is what I am supposed to do
Receives a line of input from the user, then outputs that
line to the given file. This will continue until the line input
by the user is “-1” which indicates, the end of input.
however I cannot work out the -1 part. Any help would be greatly appreciated everything else seems to work.

Answer 1

You're making things a bit more complicated than they need to be. Why C strings instead of std::string, for example? Using the right (standard-provided) classes generally leads to shorter, simpler and easier-to-understand code. Try something like this for starters:
int main()
{
std::string filename;
std::cout << "Enter filename" << std::endl;
std::cin >> filename;
std::ofstream file{filename};
std::string line;
while (std::cin >> line) {
if (line == "-1") {
break;
}
file << line;
}
}

Answer 2

First of all, the assignment asks to read a line from the user, character-wise input by get() shouldn't be the function to use. Use the member function getline() as you did to recieve the file name and use a comparison function to check against -1:
for (char line[20]; std::cin.getline(line, sizeof line) && std::cin.gcount(); )
{
if (strncmp(line, "-1", std::cin.gcount()) == 0)
break;
myFile.write(line, std::cin.gcount());
}