In file I/O, sometimes we want to input the name of a file from the keyboard. This can be done using a string since a file name is a string.

1. A string is just a sequence of characters
   
   
2. We need to declare a variable to hold a string. This can be done by the declaration:
   
   char filename[16];
   which can hold a string that contains 15 or fewer characters.
   
   
3. This type of strings (turns out to be an array of characters) is known as a cstring. The null character '\0' is used to mark the end of the cstring.
   
   
4. Strings will be dealt with in ch. 10.
   
   
5. An example is shown as follows:
   //Reads three numbers from the file specified by the user, sums the
   //numbers, and writes the sum to another file specified by the user.
   #include <fstream>
   #include <iostream>
   #include <cstdlib>
   using namespace std;
   
   int main( )
   {
       int first, second, third;
       // declare 2 character arrays for the input and output file names
       char in_file_name[16], out_file_name[16];
       ifstream in_stream;
       ofstream out_stream;
   
       cout << "I will sum three numbers taken from an input\n"
             << "file and write the sum to an output file.\n";
       cout << "Enter the input file name (maximum of 15 characters):\n";
       cin >> in_file_name;
       cout << "Enter the output file name (maximum of 15 characters):\n";
       cin >> out_file_name;
       cout << "I will read numbers from the file "
             << in_file_name << " and\n"
             << "place the sum in the file "
             << out_file_name << endl;
   
       in_stream.open(in_file_name);
       if (in_stream.fail( ))
          {
             cout << "Input file opening failed.\n";
             exit(1);
          }
   
       out_stream.open(out_file_name);
       if (out_stream.fail( ))
          {
             cout << "Output file opening failed.\n";
             in_stream.close( );        // otherwise you exit the program without closing
                                                    // the input file!
             exit(1);
          }
   
       in_stream >> first >> second >> third;
       out_stream << "The sum of the first 3\n"
             << "numbers in " << in_file_name << endl
             << "is " << (first + second + third)
             << endl;
   
       in_stream.close( );
       out_stream.close( );
   
       cout << "End of Program.\n";
       return 0;
   } //end main