Visual C++ :: Counting A Word From Text File

The user will first enter the file name to be processed. The program can do the following 5 tasks:

1. Count the number of words
2. Count the number of alphabets (without punctuation marks)
3. Count number of sentences.
4. Count the frequency of each vowel.
5. Count frequency of the following three words individually: FAST, computer and engineering

There should be a proper menu through which the user can select the desired task. The program should continue until the user asks to terminate it.

Here is what i have done so far:

#include <iostream>
#include <cstring>
#include <fstream>
#include <cstdlib>
using namespace std;
int main(void)
{
int opt=0; //option number
ifstream fin;
string filename;

[Code]...

There are a few problems.

1- When I enter option 'q', an infinite loop starts.
2- The first time, the program gives the correct value. After that, each time it gives answer ZERO.
3- The last part is not working. I experimented something which failed. I don't know how to do the last part.