Undefined reference to 'HashTable::HashTable()' - c++

Question

I'm working on a testing program for a lab and I keep getting the error
[jereminp#bondi hw3]$ make insert_test
g++ -O3 -g -o insert_test.o -c insert_test.cc
g++ -O3 -g -o insert_test insert_test.o
insert_test.o: In function `main':
/users/ugrad/2018/fall/jereminp/114/hw3/hw3/insert_test.cc:17: undefined reference to `HashTable::HashTable()'
/users/ugrad/2018/fall/jereminp/114/hw3/hw3/insert_test.cc:24: undefined reference to `HashTable::insert(int)'
/users/ugrad/2018/fall/jereminp/114/hw3/hw3/insert_test.cc:32: undefined reference to `HashTable::insert(int)'
collect2: ld returned 1 exit status
make: *** [insert_test] Error 1
I'm fairly certain I have the logic, but I can't get past this error and I feel like I'm missing something simple. Here's the parts of the code in question.
Makefile
CC = g++
CFLAGS =
COPTFLAGS = -O3 -g
insert_test: insert_test.o
$(CC) $(COPTFLAGS) -o $# $^
insert_test.cc
#include "HashTable.h"
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <string>
#include <math.h>
using namespace std;
class HashTable;
int main(int argc, char* argv[])
{
//checks .5 and .9 1x
int numRuns = 0;
int numProbes = 0;
int a=0;
HashTable h;
HashTable.hh
#ifndef HASHTABLE_H
#define HASHTABLE_H
class HashTable
{
public:
HashTable();
/* implement copy constructor, assignment, destructor if needed */
int hashfnc(int key);
int insert (int value);
/* insert the input value and return the number of probes
* return -1 if the table is full and insert fails */
bool find (int value, int& nProbes);
/* Search for the input value in table
* Return true if the search is successful, otherwise false
* Save # probes in 'nProbes' */
// getters
int capacity() { return nSlot; }
int size() { return nElem; }
double load_factor() { return load; }
int getSearchProbes() { return probesSearch; }
private:
/* declare your data */
double load; // track the load factor of table
int nSlot; // # slots i.e. max # elements can hold
int nElem; // current # elements in table
int arr[];
int probesSearch;
};
#endif
HashTable.cc
#include "HashTable.h"
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <string>
#include <math.h>
using namespace std;
class HashTable
{
public:
HashTable()
{
load = 0;
nSlot = 300;//nSlot is changable in order to optimize
nElem = 0;
arr = new int[nSlot];
probesSearch=0;
for(int i = 0;i<nSlot;i++)
{
arr[i] = NULL;
}
}
Some of the things I've tried are adding any and all includes I could think of, changing the last line shown in insert_test.cc to "HashTable h = new HashTable();"(where I got a different error), adding namespace std to the header. I feel like it should be a quick fix but at the same time I can't find the solution anywhere. Plz send help