hello. Everybody Im new in programming. Still learning. Currently I have a problem when designing a Sparse Matrix class. Class is based on a linked list which records only the non-zero elements. Source file seems to compile fine, but at a run it crashes. Debug reveals a segmentation fault, which is as far as I know connected with inproper memory allocation. However I don't seem to find the problem. This is just a base class which allows to insert non-zero elements and display them. I am using bloodshed Dev C++. Any help would be appreciated. thanks Milenkom.

Code:

#include <iostream>
using namespace std;
class Sparse
{
private:
class Elem
{
private:
int row,column;
double*elem;
Elem*next;
public:
Elem(){next=NULL;}
Elem(int a,int b,double h);
~Elem(){delete elem;}
Elem*& Next(){return next;}
double& Value()const{return *elem;}
int& Row(){return row;}
int& Column(){return column;}
};
Elem*first;
int rows;
int columns;
public:
Sparse(int,int);
~Sparse();
void Insert(int a,int b,double h);
friend ostream& operator<<(ostream&,Sparse&);
};
Sparse::Elem::Elem(int a,int b,double h)
{
elem=new double;
*elem=h;
next=NULL;
row=a;
column=b;
}
Sparse::Sparse(int a,int b):rows(a),columns(b)
{
}
Sparse::~Sparse()
{
Sparse::Elem*handy=first;
Sparse::Elem*prev;
while(handy!=NULL)
{
prev=handy;
handy=handy->Next();
delete prev;
}
}
void Sparse::Insert(int a,int b,double h)
{
Sparse::Elem*prvi=new Sparse::Elem(a,b,h);
Sparse::Elem*handy;
if(first==NULL)
{
first=prvi;
}
else
{
handy=first;
while(handy->Next()!=NULL)
{
handy=handy->Next();
}
handy->Next()=prvi;
}
}
ostream& operator<<(ostream &os,Sparse &s)
{
for(int j=1;j<=s.columns;j++)
{
for(int i=1;i<=s.rows;i++)
if(s.first->Column()==j && s.first->Row()==i)
{
cout<<s.first->Value()<<" ";
s.first=s.first->Next();
}
else
cout<<0<<" ";
cout<<"\n";
}
return os;
}
int main()
{
Sparse s1(10,10);
s1.Insert(1,1,10);
s1.Insert(2,1,20);
s1.Insert(3,2,30);
cout<<s1;
system("PAUSE");
return 0;
}