Undefined reference to `Vector::SetElem(int, double)'|

#include<stdio.h>
#include<conio.h>
#include<iostream>
#include<math.h>
#include "vector.h"
 
using namespace std;
 
int main ()
{
    Vector a;
    a.SetElem(0,1.5);
    a.SetElem(1, 2.3);
    a.SetElem(2, 8.2);
    cout << "\npress any key to exit...";
    getch();
}

#ifndef _VECTOR_H
#define _VECTOR_H
 
class Vector
{
protected:
    double *p; // values
    int n; // size
    protected:
    /// Utilites
    void GetMem(){ p=new double [n];}
//    static inline void Vector::Error(char *str)
public:
    /// Constructors/destructor
    Vector(int _n=3);
    Vector(Vector const &src);
    Vector(double x);
    Vector(double x, double y);
    Vector(double x, double y, double z);
    Vector(int _n, double *v);
    ~Vector();
    /// Properties
    inline int GetN() const;
    inline double GetLength() const;
    inline double GetElem(int i) const;
    inline void SetElem(int i, double v);
    static inline void Error(char *str);
    /// Operations
    void Add(Vector const &v);
    void Multiply(double a);
    void Print() const;
    void Input();
 
};
#endif // #ifndef _VECTOR_H

#include<stdio.h>
#include<conio.h>
#include<iostream>
#include<math.h>
#include "vector.h"
#include <cstdlib>
using namespace std;
/********************************************************
// Public interface methods
********************************************************/
// C O N S T R U C T O R S / D E S T R U C T O R
/////////////////////////////////////////////////////////
// recieves size (number of items), can be default-constructor
Vector::Vector(int _n) :n(_n)
{
if(n<=0) Error("bad vector size");
GetMem();
}
/////////////////////////////////////////////////////////
// If takes double, makes 2-D vector
Vector::Vector(double x) :n(2)
{
GetMem();
p[0]=p[1]=x;
}
/////////////////////////////////////////////////////////
// If takes two doubles, makes 2-D vector
Vector::Vector(double x, double y) :n(2)
{
GetMem();
p[0]=x;
p[1]=y;
}
/////////////////////////////////////////////////////////
// If takes tree doubles, makes 3-D vector
Vector::Vector(double x, double y, double z) :n(3)
{
GetMem();
p[0]=x;
p[1]=y;
p[2]=z;
}
///////////////////////////////////////////////////////////Makes vector
Vector::Vector(int _n, double *v) :n(_n)
{
if(n<=0) Error("bad vector size");
GetMem();
for(int i=0; i<n; i++) p[i]=v[i];
}
///Destructor
Vector::~Vector()
{
delete p;
}
// P R O P E R T I E S
/////////////////////////////////////////////////////////
// returns number of elements
inline int Vector::GetN() const
{
return n;
}
inline void Vector::Error(char *str)
{
    std::cout << str;
    exit(1);
}
/////////////////////////////////////////////////////////
// returns vector length
double Vector::GetLength() const
{
double s=0;
for(int i=0; i<n; i++) s+= (p[i]*p[i]);
return sqrt(s);
}
/////////////////////////////////////////////////////////
// returns vector's i-element
double Vector::GetElem(int i) const
{
if(i<0 || i>=n) Error("bad index");
return p[i];
}
/////////////////////////////////////////////////////////
// sets vector's i-element’s value
void Vector::SetElem(int i, double v)
{
    if(i<0 || i>=n) Error("bad index");
    p[i]=v;
}
 
// O P E R A T I O N S
void Vector::Add(Vector const &v)
{
if(n!=v.n) Error("Bad vector size");
for(int i=0; i<n; i++) p[i]+=v.p[i];
}
void Vector::Multiply(double a)
{
for(int i=0; i<n; i++) p[i]*=a;
}
void Vector::Print() const
{
cout << "Vector (" << p[0];
for (int i=1; i<n; i++) cout << "; " << p[i];
cout << ") ";
}
void Vector::Input()
{
cout << "Input vector elements:\n";
for (int i=0; i<n; i++)
{
cout << "v["<< i << "] = ";
cin >> p[i];
}
}
/********************************************************
// F R I E N D F U N C T I O N S
********************************************************/