How to add elements to a vector

im trying to add elements to a vector in my program. but im not sure if im doin it right. so far what i have below does not work. i get an error that says error LNK2019: unresolved external symbol "public: __thiscall MySet::MySet(void)" (??0MySet@@QAE@XZ) referenced in function _main

#include <iostream>
#include <map>
#include <vector>

using namespace std;

class MySet{


public:
 vector<int> elements;
 MySet();
 void addElement(int value);
 int removeElement(int index);
 int sum();
 int size();
  };




void MySet::addElement(int value){
  elements.push_back(value);

}
int main(int argc, char *argv[]){
  int value;
  MySet set;
  cout << "Enter your numbers " << endl;
  cin >> value;
  while(value != -1){
  set.addElement(value);
 }

  system("PAUSE");
}