#include <fstream>
#include <iostream>
 
using namespace std;
 
int main()	// returns 1 on error
{
	char fileName[80];
	char buffer[255]; // for user input.
	cout << "Please reenter the file name: ";
	cin >> fileName;
 
	ifstream fin(fileName);
 
	if (fin) // allready exists ?
	{
		cout << "Current file contents:\n";
		char ch;
 
		while (fin.get(ch))
			cout << ch;
		cout << "\n***End of file contents.***\n";
	}
	fin.close();
 
	cout << "\nOpening " << fileName << " in append mode...\n";
 
	ofstream fout(fileName, ios::app);
	if (!fout)
	{
		cout << "Unable to open " << fileName << " for appending !\n";
		return 1;
	}
 
	cout << "\nEnter text for this file: ";
	cin.ignore(1, '\n');
	cin.getline(buffer, 255);
	fout << buffer << "\n";
	fout.close();
 
	fin.open(fileName); // reassign existing fin object.
	if (!fin) // <-- problem is here.
	{
		cout << "Unable to open " << fileName << " for reading !\n";
		return 1;
	}
 
	cout << "\nHere's the contents of the file: \n";
	char ch;
	while (fin.get(ch))
		cout << ch;
	cout << "\n***End of file contents.***\n";
	fin.close();
 
	return 0;
}

if (fin) // allready exists ?
	{
		cout << "Current file contents:\n";
		char ch;
 
		while (fin.get(ch))
			cout << ch;
		cout << "\n***End of file contents.***\n";
	}
	fin.close();
	fin.clear();
 
.......