In a program I am writing, I wrote for two classes (Coordinate, and Graph), with one of them taking the other as constructor arguments. When I try to compile it I get the following error for Graph.cpp:

Undefined symbols: "Graph::Coordinate::Coordinate(double)", referenced from: Graph::Graph() in Graph.o Graph::Graph() in Graph.o "Graph::Coordinate::Coordinate()", referenced from: Graph::Graph(Graph::Coordinate, Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate, Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate)in Graph.o Graph::Graph(Graph::Coordinate)in Graph.o Graph::Graph() in Graph.o Graph::Graph() in Graph.o Graph::Graph() in Graph.o Graph::Graph() in Graph.o Graph::Graph() in Graph.o Graph::Graph() in Graph.o ld: symbol(s) not found collect2: ld returned 1 exit status

I checked the code and couldn't find anything out of the ordinary. Here are the four class files: (Sorry if it's a lot of code to sift through.)

Coordinate.h

class Graph{
#include "Coordinate.h"
public:
 Graph();
 Graph(Coordinate);
 Graph(Coordinate, Coordinate);
 Graph(Coordinate, Coordinate, Coordinate);

 void setXSize(int);
 void setYSize(int);

 void setX(int); //int corresponds to coordinates 1, 2, or 3
 void setY(int);
 void setZ(int);

 int getXSize();
 int getYSize();

 double getX(int); //int corresponds to coordinates 1, 2, or 3
 double getY(int);
 double getZ(int);

 void outputGraph();
 void animateGraph();


private:
 int xSize;
 int ySize;

 Coordinate coord1;
 Coordinate coord2;
 Coordinate coord3;

};

Coordinate.cpp

#include <iostream>
#include "Coordinate.h"


Coordinate::Coordinate()
{
 xCoord = 1;
 yCoord = 1;
 zCoord = 1;

 xVel = 1;
 yVel = 1;
 zVel = 1;
}
Coordinate::Coordinate(double xCoo)
{
 xCoord = xCoo;
 yCoord = 1;
 zCoord = 1; 

 xVel = 1;
 yVel = 1;
 zVel = 1;
}
Coordinate::Coordinate(double xCoo,double yCoo)
{
 xCoord = xCoo;
 yCoord = yCoo;
 zCoord = 1;  

 xVel = 1;
 yVel = 1;
 zVel = 1;
}
Coordinate::Coordinate(double xCoo,double yCoo,double zCoo)
{
 xCoord = xCoo;
 yCoord = yCoo;
 zCoord = zCoo;  

 xVel = 1;
 yVel = 1;
 zVel = 1;
}

void Coordinate::setXCoord(double xCoo)
{
 xCoord = xCoo;
}
void Coordinate::setYCoord(double yCoo)
{
 yCoord = yCoo; 
}
void Coordinate::setZCoord(double zCoo)
{
 zCoord = zCoo;
}
void Coordinate::setXVel(double xVelo)
{
 xVel = xVelo;
}
void Coordinate::setYVel(double yVelo)
{
 yVel = yVelo;
}
void Coordinate::setZVel(double zVelo)
{
 zVel = zVelo;
}


double Coordinate::getXCoord()
{
 return xCoord;
}
double Coordinate::getYCoord()
{
 return yCoord;
}
double Coordinate::getZCoord()
{
 return zCoord;
}
double Coordinate::getXVel()
{
 return xVel;
}
double Coordinate::GetYVel()
{
 return yVel;
}
double Coordinate::GetZVel()
{
 return zVel; 
}

Graph.h

class Graph{
#include "Coordinate.h"
public:
 Graph();
 Graph(Coordinate);
 Graph(Coordinate, Coordinate);
 Graph(Coordinate, Coordinate, Coordinate);

 void setXSize(int);
 void setYSize(int);

 void setX(int); //int corresponds to coordinates 1, 2, or 3
 void setY(int);
 void setZ(int);

 int getXSize();
 int getYSize();

 double getX(int); //int corresponds to coordinates 1, 2, or 3
 double getY(int);
 double getZ(int);

 void outputGraph();
 void animateGraph();


private:
 int xSize;
 int ySize;

 Coordinate coord1;
 Coordinate coord2;
 Coordinate coord3;

};

Graph.cpp

#include "Graph.h"
#include "Coordinate.h"
#include <iostream>
#include <ctime>

using namespace std;

Graph::Graph()
{
 Coordinate coord1(0);
}
Graph::Graph(Coordinate cOne)
{
 coord1 = cOne;

 xSize = 20;
 ySize = 20;
}
Graph::Graph(Coordinate cOne, Coordinate cTwo)
{
 coord1 = cOne;
 coord2 = cTwo;

 xSize = 20;
 ySize = 20;
}
Graph::Graph(Coordinate cOne, Coordinate cTwo, Coordinate cThree)
{
 coord1 = cOne;
 coord2 = cTwo;
 coord3 = cThree;

 xSize = 20;
 ySize = 20;
}

void Graph::setXSize(int size)
{
 xSize = size;
}
void Graph::setYSize(int size)
{
 ySize = size;
}

int Graph::getXSize()
{
 return xSize; 
}
int Graph::getYSize()
{
 return ySize; 
}

void Graph::outputGraph()
{

}
void Graph::animateGraph()
{

}

Thanks very much for any help!