File input/output is part of Short Circuit's Console Program Basics selection.
Task

Create a file called   "output.txt",   and place in it the contents of the file   "input.txt",   via an intermediate variable.

In other words, your program will demonstrate:

   how to read from a file into a variable
   how to write a variable's contents into a file


Oneliners that skip the intermediate variable are of secondary interest — operating systems have copy commands for that.




#include <iostream>
#include <fstream>
#include <string>
 
using namespace std;
 
int main() {
    string line;
    ifstream input ( "input.txt" );
    ofstream output ("output.txt");
 
    if (output.is_open()) {
        if (input.is_open()){
            while (getline (input,line)) {
                output << line << endl;
            }
            input.close(); // Not necessary - will be closed when variable goes out of scope.
        }
        else {
            cout << "input.txt cannot be opened!\n";
        }
        output.close(); // Not necessary - will be closed when variable goes out of scope.
    }
    else {
        cout << "output.txt cannot be written to!\n";
    }
    return 0;
}