Text File Analyzer c++ [on hold]

My question is how do I get a text file for input/output on my computer. This is my code so far which makes since to me but I need to get a text file! How do I make one...How do I access one...How can I get it to work in my program to read characters, letters, digits, etc...Do I need permission's to access?

#include <iostream>
#include <fstream>
#include <cctype>
#include <cstring>
using namespace std;

int main()
{
    char filename[30];      // a string for filenames
    ifstream input;         // a file input stream
    ofstream output;        // a file output stream

    do
    {
        input.clear();      // to clear status flags in the stream
        cout << "Please enter the name of the input file.\n";
        cout << "Filename: ";
        cin >> filename;
        input.open(filename);
        if (!input)
            cout << "Sorry not a valid file. Try again!\n";
    } while (!input);


    do
    {
        output.clear();     // to clear status flags in the stream
        cout << "Please enter the name of the output file.\n";
        cout << "Filename: ";
        cin >> filename;
        output.open(filename);
        if (!output)
            cout << "Sorry not a valid file. Try again!\n";
    } while (!output);


    char ch;
    int characters = 0;
    int letters = 0;
    int white_space = 0;
    int digits = 0;
    int other_characters = 0;
    int uppercase = 0;
    int lowercase = 0;

    while (!input.eof());   // while not end of input file
    {
        input.get(ch);

        if(isalnum(ch))
            characters++;
        output << ch;

        if(isalpha(ch))
            ++letters;
        output << ch;

        if(isspace(ch))
            ++white_space;
        output << ch;

        if(isdigit(ch))
            ++digits;
        output << ch;

        if(ispunct(ch))
            ++other_characters;
        output << ch;

    }
    double perc_letters = 0;
    double perc_white_space = 0;
    double perc_digits = 0;
    double perc_other_characters = 0;

    cout << "\nStatistics for file:" << filename << endl;
    cout << "--------------------------------------------------\n";

    cout << "Total # of charcters in file:\t " << characters << endl;
    cout << "\nCategory\tHow many in file\t% of file\n";
    cout << "--------------------------------------------------\n";
    cout << "Letters\t" << letters << "\t" << perc_letters << "%" << endl;
    cout << "White space\t" << white_space << "\t" << perc_white_space << "%" << endl;
    cout << "Digits\t" << digits << "\t" << perc_digits << "%" << endl;
    cout << "Other characters\t" << other_characters << "\t" << perc_other_characters << "%" << endl;
    cout << "\n";

    input.close();
    output.close();

    return 0;

}