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I'm trying to set up a couple classes, but I'm getting an error: Linker error - Undefined reference to 'Node::~Node()'. I think it might have something to do with how my headers are set up, but I'm unsure what I need to do to fix it. (FYI I added using std to try to fix some other problems, although it's not necessary).

Thanks.

Line.h

```
#ifndef LINE_H
#define LINE_H
#include "Node.h"
using namespace std;
class Line
{
public:
double m; //slope
double b; //y-int
Line(Node p, Node q)
{
m = ((double)(p.r-q.r))/((double)(p.c-q.c));
b = p.r-(m*q.c);
}
double getr(int c)
{
return m*c+b;
}
double getc(int r)
{
return (r-b)/m;
}
~Line();
};
#endif
```

Node.h

```
#ifndef NODE_H
#define NODE_H
#include <vector>
using namespace std;
class Node
{
public:
int status; //process status
int r,c; //xy coords
vector<Node> neighbors; //list of neighbors
vector<double> distances; //distance between this node and node in neighbors.at(i)
Node(void)
{
r = 0;
c = 0;
status = 0;
}
Node(int newr, int newc)
{
r = newr;
c = newc;
status = 0;
}
void add(Node newneighbor,double dist)
{
neighbors.push_back(newneighbor);
distances.push_back(dist);
}
~Node();
};
#endif
```

Driver.cpp

```
#include <iostream>
#include <vector>
#include <math.h>
#include "Node.h"
#include "Line.h"
using namespace std;
Node find(char c); //search grid for character c and return a node with grid coordinates
bool isCorner(int r, int c, int newr, int newc); //test if cell (newr,newc) is an empty corner of cell (r,c)
bool isFree(double r, double c); //test if cells containing (r,c) are empty
bool validLine(Node a, Node b); //test whether a line can be drawn from node a to node b without intersecting walls
void link(Node a, Node b, double dist); //link two nodes together with a distance dist
double dist_form(Node a, Node b); //distance between two nodes
bool isValid(double r, double c); //test if intersecting cells of point (r,c) are empty
int G_ROWS = 6;
int G_COLS = 10;
char* grid[] = {" ",
" # ",
" # ",
" s # e ",
" # ",
" "};
Node start = find('s');
Node end = find('e');
//stores all nodes
vector<Node> graph;
int main()
{
graph.push_back(start);
//create nodes
for (int r=0; r<G_ROWS; r++)
for (int c=0; c<G_COLS; c++)
{
if (isCorner(r,c,r+1,c+1))
graph.push_back(Node(r+1,c+1));
if (isCorner(r,c,r+1,c-1))
graph.push_back(Node(r+1,c));
if (isCorner(r,c,r-1,c+1))
graph.push_back(Node(r,c+1));
if (isCorner(r,c,r-1,c-1))
graph.push_back(Node(r,c));
}
graph.push_back(end);
//link nodes
for (int i=0; i<graph.size()-1; i++)
for (int j=i+1; j<graph.size(); j++)
if (validLine(graph.at(i),graph.at(j)))
link(graph.at(i),graph.at(j),dist_form(graph.at(i),graph.at(j)));
//print out data
for (int i=0; i<graph.size(); i++)
cout << " " << graph.at(i).r << ", " << graph.at(i).c << "\n";
system("pause");
return 0;
}
//finds the first cell with value c and returns the node of that cell
Node find(char c)
{
for (int r=0; r<G_ROWS; r++)
for (int c=0; c<G_COLS; c++)
if (grid[r][c]==c) return(Node(r,c));
return (Node(-1,-1));
}
//test whether cell (newr,newc) is an empty corner of cell (r,c)
bool isCorner(int r, int c, int newr, int newc)
{
//check boundaries
if (newr<0 || newr>=G_ROWS || newc<0 || newc>=G_COLS) return false;
if (grid[newr][newc]!=' ') return false;
//check if valid corner location
int difr = r-newr;
int difc = c-newc;
if (abs(difr)!=1 || abs(difc)!=1) return false;
//test bordering cells
return (grid[newr+difr][newc]==' ' && grid[newr][newc+difc]==' ');
}
//test if cells that contain point (r,c) are empty
bool isFree(double r, double c)
{
for (double newr=r; int(newr)>=0; newr--)
for (double newc=c; int(newc)>=0; newc--)
if (grid[int(newr)][int(newc)]!=' ') return false;
return true;
}
//test if nodes are valid neighbors (aka: line can be drawn between them
bool validLine(Node a, Node b)
{
//find line to place points on
Line myLine(a,b);
for (int i=min(a.c,b.c); i<max(a.c,b.c); i++)
if (!isValid(i,myLine.getc(i))) return false;
for (int i=min(a.r,b.r); i<max(a.r,b.r); i++)
if (!isValid(myLine.getr(i),i)) return false;
return true;
}
//link two nodes togethr as neighbors with distance dist
void link(Node a, Node b, double dist)
{
a.add(b,dist);
b.add(a,dist);
}
double dist_form(Node a, Node b)
{
return sqrt(pow(a.c-b.c,2) + pow(a.r-b.r,2));
}
//test is intersecting cells of (r,c) are empty
bool isValid(double r, double c)
{
for (double newr=r; int(newr)>=0; newr--)
for (double newc=c; int(newc)>=0; newc--)
if (grid[int(newr)][int(newc)]!=' ') return false;
return true;
}
```