help regarding Linked list

[T.N.Sharma]

Hi
I am trying to generated a Huff man code.
i am trying to arrange a vector<info> (info is a structure) to get a binary tree.
0. Read a txt file containing about 10 to 20 different symbols.and store it in a vector (vector <info>);
1. First sort the vector according to occur (occur is an interger value in info).
2. Pick up the last two elements of vector <info> and attach it to a new info type structure.
3. Remove last two elements form the vector mentioned above.
4. append the new formed info type structure at the end and repeat the same.

I doubt my append function (given in the code below).
And the Code_fun function(given below) gives a segmentation fault.
Pleas help
My code is given Below.

#include<iostream>
#include<fstream>
#include<string>
#include<vector>
#include<algorithm>
using namespace std;

struct info {
	char ch;
	int occur;
	info *Right;
	info *Left;
	info *Head;
};

struct Code{
	char Ch;
	string Co;
};

vector<Code> Store_code;
vector<Code> ::iterator it1;
Code nw_code;

vector<info> Read_txt()
{
	ifstream infi;
	ofstream onfi;
	char c;
	vector<info> letter;
	info  n_letter;
	vector<info>::iterator it;
	infi.open("hi1.txt");
	
	while(!infi.eof()){
		infi>>c;
		it = letter.begin();
		while(it != letter.end()) {
			if ((*it).ch==c){
				(*it).occur ++;
				break;
			}
			else 
				it++;
		}
		if (it==letter.end()){
			n_letter.ch = c;
			n_letter.occur = 1;
			letter.push_back(n_letter);
		}
			
	}
	infi.close();
//	for(it=letter.begin(); it!=letter.end(); it++)
//		cout<<(*it).ch<<"\t"<<(*it).occur<<endl;
	return letter;		

}

void Sort(vector<info> &letter)
{
	vector<info>::iterator it1, it2, it3;

	for(it1=letter.begin(); it1!=letter.end()-1; it1++)
		for(it2=it1; it2!=letter.end(); it2++) {
			if((*it2).occur > (*it1).occur){
				swap((*it1).occur,(*it2).occur);
				swap((*it1).ch, (*it2).ch);
			}
				
		}
}

void Append(vector<info> &letter)
{
	info *nw_node;
	int x,y;

	while(letter.begin() != letter.end()-1){
		Sort(letter);
		nw_node = new info;
	
		x=letter.back().occur;
	
	//	letter.back().Head = nw_node;
		nw_node->Left = &letter.back();

	
		letter.pop_back();

		y=letter.back().occur;
	//	letter.back().Head = nw_node;
		nw_node->Right = &letter.back();
		letter.pop_back();
		nw_node->occur = x+y;
		nw_node->ch = 'x';
		letter.push_back(*nw_node);
		cout<<letter.back().Left->ch<<"\t"<<letter.back().Left->occur<<endl;
		cout<<letter.back().Right->ch<<"\t"<<letter.back().Right->occur<<endl;
	}
}

/*	
void Code_fun(info &letter)
{
	string str;
	cout<<endl<<letter.Left->ch<<endl;
	if(letter.ch == 'x') {
	cout<<endl<<letter.Left->ch<<endl;
	letter=*letter.Left;
	cout<<endl<<letter.Left->ch<<endl;	
	cout<<endl<<letter.Right->ch<<endl;	
}
		str.push_back('1');
	
		
		Code_fun(*letter.Left);
	
		nw_code.Ch = letter.Left->ch;
		nw_code.Co = str;
		Store_code.push_back(nw_code);
		str.erase(str.end());
		str.push_back('0');
		exit(0);	

		Code_fun(*letter.Right);
	
		nw_code.Ch = letter.Right->ch;
		cout<<letter.Right->ch<<"\t";
		nw_code.Co = str;
		cout<<"str"<<endl;
		Store_code.push_back(nw_code);
		str.erase(str.end());
	}

}
*/			


int  main()
{
	vector<info> tter;
	info tter1;
	vector<info>::iterator it;
//	vector<Code>::iterator it1;
	tter = Read_txt();
	Sort(tter);


	for(it=tter.begin(); it!=tter.end(); it++)
		cout<<(*it).ch<<"\t"<<(*it).occur<<endl;
//		init(tter.back());

	Append(tter);

	for(it=tter.begin(); it!=tter.end(); it++)
		cout<<(*it).ch<<"\t"<<(*it).occur<<endl;
	tter1 = tter[0];
//	Code_fun(tter1);
	for(it1=Store_code.begin(); it1!=Store_code.end(); it1++)
		cout<<(*it1).Ch<<"\t"<<(*it1).Co<<endl;




	return 0;
}