ld returned 1 exit status (Structures and Header files in C++)

Question

I am learning structures, pointers, and header files in c++. I have begun a project that I found on the internet and am getting stuck very early on. Here is the error:

undefined reference to `readPoly(Polygon&)' collect2.exe: error: ld returned 1 exit status

and the code of all the included files:

Main:

#include <iostream> // C++ input/output library
#include "Point.h"
#include "Polygon.h"

using namespace std;

int main() 
{
   struct Point vertices[20];
   struct Polygon poly[10];
   char command;
   int counter = 0;
   while(1)
   {
      cout << "Enter command (A | P | T | X): ";
      cin >> command;

      while(command != 'A' && command != 'a' && command != 'P' && command != 'p' && command != 'T' && command != 't' && command != 'X' && command != 'x')
      {
         cout << "Improper command. Try again: ";
         cin >> command;
      }

      switch(command)
      {
         case 'A': case 'a':   
            readPoly(poly[10]);
         case 'P': case 'p':
            break;
         case 'T': case 't':
            break;
         case 'X': case 'x':
            return 0;
      }
   }  
}

Polygon.h:

struct Polygon
{
   struct Point vertices[10];
   int verts;
};

void printPoly(Polygon &pol);

void readPoly(Polygon &pol);

Point.cpp:

#include "Point.h"

void printPoint(Point &pt)
{

}

void readPoint(Point &pt)
{
}

Point.h:

struct Point 
{
   double x; // X coordinate
   double y; // Y coordinate
};

void printPoint(Point &pt);
void readPoint(Point &pt);