linker error

[cash]

I'm getting a linker error in my code and I don't know why?

Header

  
#undef WATCH_H
#ifndef WATCH_H
#define WATCH_H

#include <time.h>
class watch
{
public:
    watch();
    void start();
    void stop();
    void delay(int duration);
    float seconds();
    float minutes();
    float hours();
    
private:
    clock_t ticks_passed;
};


#endif /* WATCH_H_hpp */ 

driver file

#include <iostream>
#include <stdlib.h>
#include "WATCH_H.hpp"
using namespace std;
watch :: watch()
{
    ticks_passed = clock();
    
}
 void watch:: start()
{
    ticks_passed = clock();
}
 void watch:: stop()
{
    ticks_passed = clock() - ticks_passed;
    if(ticks_passed == clock_t(-1))
    {
        cout << "Clock overflow" << endl;
        exit(1);
    }
    
}
void watch:: delay(int duration)
{
    for(int i =0; i<duration; ++i);
        
}

float watch:: seconds()
{
    return float(ticks_passed)/CLOCKS_PER_SEC;
}

float watch :: minutes()
{
    return float(ticks_passed)/CLOCKS_PER_SEC/60;
}
float watch :: hours()
{
    return float(ticks_passed)/CLOCKS_PER_SEC/60/60;
}

Implementation

#include <iostream>
#include <ctime>
#include <vector>
#include <iomanip>
#include <algorithm>
#include "WATCH_H.hpp"

const int SIZE =10000;
unsigned int seed = (unsigned)time(0);
using namespace std;
void bubble_sort(vector <int>v);
double random (unsigned int &seed);
void initialize_vector(vector<int> &v);
void print_vector (vector<int> :: iterator b,
                   vector<int> :: iterator e );
int main()
{
    vector <int> v;
    watch my_watch;
    initialize_vector(v);
    my_watch.start();
    bubble_sort(v);
    my_watch.stop();
    print_vector(v.begin(), v.end());
    cout << "Seconds passed " << my_watch.seconds()<< endl;
   
    my_watch.start();
    sort(v.begin(),v.end());
    my_watch.stop();
    print_vector(v.begin(), v.end());
    cout << "Seconds passed " << my_watch.seconds()<< endl;
    return 0;
}
void initialize_vector(vector<int> &v)
{
    for (int i=0; i<SIZE; i++)
        v.push_back(random(seed)*11);
}
void bubble_sort(vector<int> &v)
{
    int temp;
    for(int k=1; k<v.size()-1; ++k)
        for(int j=0;j<v.size()-1-k;++j)
            if(v[j]>v[j+1])
            {
                temp= v[j];
                v[j]=v[j+1];
                v[j+1] = temp;
            }
}
double random(unsigned int &seed)
{
    const int MODULUS = 15749;
    const int MULTIPLIER = 69069;
    const int INCREMENT = 1;
    seed = ((MULTIPLIER*seed)+INCREMENT)%MODULUS;
    return double (seed)/MODULUS;
}

void print_vector (vector<int> :: iterator b,
                   vector<int> :: iterator e )
{
    vector<int> :: iterator p =b;
    while(p<e)
        cout << setw(3) << (*p++);
    cout << endl;
}

[fiji885]

You prototype the bubble sort function as
void bubble_sort(vector<int>& v)

but you implement it as
void bubble_sort(vector<int> v)