Question

Given list.h, main.cpp, i need to write list.cpp. having a lot of problems. please help.

list.h:

//////////////////////////////////////////////////////////////////////////
#ifndef LIST_H
#define LIST_H
//////////////////////////////////////////////////////////////////////////

namespace CS170
{
struct node
{
int value;
node *next;
};

class list
{
public:
// Constructor for list. Creates an empty list
list();

/* Destructor for list.
Empty the list and release the allocated memory
*/
~list();

// Prints out the values contained in the list
void print_list() const;

// Returns the current size of the list
unsigned size() const;

// Returns true if list is empty, false otherwise
bool empty() const;
  
// Frees (deletes) all of the nodes in the list
void clear();

/* Creates a node with val and
add it to the front of the list */
void push_front(int val);

// Return the first node in the list
node *front();

/* Removes nodes at position pos.
Position count starts from zero.
*/
void erase(int pos);

/* Removes nodes from position first to position last-1.
Position count starts from zero.
*/
void erase(int first, int last);

/* Resizes the list to contain n elements.
If n is smaller than the current size, then keep only
the first n elements, then destroy those beyond.
If n is larger than the current size, the new elements
are initialized as val.
*/
void resize(int n, int val = 0);

// Sorts the list ascendingly
void sort();
  
/* Assume the current list and l2 are both sorted ascendingly,
this function merges them into one, so that the elements
are still in ascending order.
The current list will store the merged elements,
while l2 will become empty.
*/
void merge(list &l2);

private:
unsigned list_size;
node *the_list;

node *make_node(int val);
};
}
#endif // LIST_H

main.cpp:

#include <fstream>
#include <iostream>
#include "list.h"

CS170::list& read_list_push_front(const char *filename,CS170::list &l)
{
int value;
std::ifstream fin(filename);
if (!fin.is_open())
std::cout <<filename<< " is not found!" << std::endl;
else
while (!fin.eof())
{
fin >> value;
l.push_front(value);
}

return l;
}

int main(int argc, char *argv[])
{
if(argc<2)
{   
std::cerr<<"Usage: "<<argv[0]<<" <filename>\n";
return 1;
}
CS170::list l1, l2;

l1 = read_list_push_front(argv[1],l1);
std::cout << "l1:\n";
l1.print_list();
  
std::cout << "\nErase l1 at 100:\n";
l1.erase(100);
l1.print_list();
  
std::cout << "\nErase l1 at 200:\n";
l1.erase(200);
l1.print_list();

std::cout << "\nErase l1 from 100 to before 200:\n";
l1.erase(100, 200);
l1.print_list();

std::cout << "\nResize l1 to 500 elements, fill with 100:\n";
l1.resize(500, 100);
l1.print_list();

std::cout << "\nResize l1 to 200 elements:\n";
l1.resize(200);
l1.print_list();
  
std::cout << "\nSort l1:\n";
l1.sort();
l1.print_list();
  
std::cout << "\nl2:\n";
l2 = read_list_push_front(argv[1],l2);
l2.print_list();
  
std::cout << "\nSort l2:\n";
l2.sort();
l2.print_list();
  
l1.merge(l2);
std::cout << "\nl1 after merging:\n";
l1.print_list();
std::cout << "\nl2 after merging:\n";
l2.print_list();
  
l1.clear();
l2.clear();
  
return 0;
}