#include <fiostream.h>
    int main () {
        ofstream out("out.txt");
        if (out.is_open()) 
       {
            out << "This is a line.\n";
            out.close();
        }
      return 0;
      
 // reading a text file
    #include <iostream.h>
    #include <fstream.h>
    #include <stdlib.h>
    
    int main () {
        char buffer[256];
        ifstream in("test.txt");
        if (! in.is_open())
        { cout << "Error opening file"; exit (1); }
        while (!in.eof() )
        {
            in.getline (buffer,100);
            cout << buffer << endl;
        }
        return 0;

#define name2str(name) (#name)

    #define xstr(s) str(s)
     #define str(s) #s
     #define foo 4
     str (foo)
          ==> "foo"
     xstr (foo)
          ==> xstr (4)
          ==> str (4)
          ==> "4"