Смена оператора заявления

Я сделал некоторые изменения, и теперь у меня возникла проблема с моим оператором switch. Функции должны читать файлы произвольного доступа. Когда я запускаю программу, она отображает меню, а когда я выбираю опцию, она выводит только первую опцию, которую я выберу. Если я выбираю другой вариант, он не выводит буквы. Как я могу это исправить?

//Random-Access Files Program
//This program reads a file from beg to end, end to beg, beg to 4th position,
//8th to 15th position, end to 21st position, and 22nd position to the end

#include <iostream>
#include <fstream>

using namespace std;

void begToEnd(fstream &, char);
void endToBeg(fstream &, char);
void begTo4th(fstream &, char);
void eighthTo15th(fstream &, char);
void endTo21st(fstream &, char);
void Twenty2ndToEnd(fstream &, char);

int main()
{
char letters;   //holds the character
int choice;

fstream file("alphabet.txt", ios::in | ios::binary);  //This opens the file

do
{
cout << "Enter 1 to read from beginning to end" << endl
<< "Enter 2 to read from end to beginning" << endl
<< "Enter 3 to read from beginning to 4th position" << endl
<< "Enter 4 to read from 8th to 15th position" << endl
<< "Enter 5 to read from end to 21st position" << endl
<< "Enter 6 to read from 22nd position to the end" << endl;

cin >> choice;

switch(choice)
{
case 1:
begToEnd(file, letters);
break;
case 2:
endToBeg(file, letters);
break;
case 3:
begTo4th(file, letters);
break;
case 4:
eighthTo15th(file, letters);
break;
case 5:
endTo21st(file, letters);
break;
case 6:
Twenty2ndToEnd(file, letters);
break;
}

cout << endl;

system("pause");

file.close(); //Closes the file
}

while(choice != 'N' && choice != 'n');
return 0;

}
void begToEnd(fstream &in, char letter)
{
in.seekg(0L, ios::beg);  //Displays beginning to end
for(int i = 0; i < 25; i++)
{
in.get(letter);
cout <<"Beginning to end: " << letter << endl;
}
}

void endToBeg(fstream &in, char letter)
{
in.seekg(0, ios::end);  //Displays end to beginning
int size = in.tellg();
for (int i=1; i <= size; i++)
{
in.seekg(-i, ios::end);
letter=in.get();
cout << "End to beginning: " << letter << endl;
}
}

void begTo4th(fstream &in, char letter)
{
in.seekg(0L, ios::beg);  //Displays beginning to 4th position
for(int i = 0; i < 4; i++)
{
in.get(letter);
cout << "Beginning to the 4th letter: " << letter << endl;
}
}

void eighthTo15th(fstream &in, char letter)
{
in.seekg(7L, ios::beg);  //Displays 8th to 15th position
for(int i = 0; i < 7; i++)
{
in.get(letter);
cout << "8th to 15th letter: " << letter << endl;
}
}

void endTo21st(fstream &in, char letter)
{
in.seekg(0, ios::end);  //Displays end to 21st position
int size = in.tellg();
for (int i=1; i <= 5; i++)
{
in.seekg(-i, ios::end);
letter=in.get();
cout << "End to 21st: " << letter << endl;
}
}

void Twenty2ndToEnd(fstream &in, char letter)
{
in.seekg(21L, ios::beg);  //Displays the 22nd position to the end
for(int i = 0; i < 5; i++)
{
in.get(letter);
cout << "22nd to end: " << letter << endl;
}
}