#include <iostream>
#include <fstream>
#include <ostream>
#include <windows.h>

/*
    Letter (Letter | Digit)*
*/

using namespace std;

int main()
{
    fstream text("D:\\text.txt");

    if (!text)
    {
        cout << "Error!\n";
        exit(-1);
    }

    char in;
    string var_name;
    in = text.get();
    cout << "in = " << in << endl;

    if (isalpha(in))
    {
        var_name += in;
        cout << "var_name = " << var_name << endl;
    }
    else
    {
        cout << "Error!\n";
        exit(-1);
    }

    in = text.get();
    cout << "second in = " << in << endl;

    while ((isalpha(in) || isdigit(in)) && (!text.eof()))
    {
        var_name += in;
        in = text.get();
        cout << "\nin = " << in;
    }

    cout << "\nvar_name = " << var_name << endl;
    text.close();
    return 0;
}