Ошибка линковки

#include "stdafx.h"
#include "Head1.h"
#include "iostream"
#include "cmath"
#include "conio.h"
#include "stdio.h"
#include "stdlib.h"
 
 
 
void main()
{
   double a=0;
   double b=0;
   int n=0;
   cout<<'a';
   cin>>a;
   cout<<'b';
   cin>>b;
   cout<<'n';
   cin>>n;
   double s=0;
   int m=3;
 
switch(m){
case '1':{
    s+=integrals(a,b,n,f,rect);
    }
    break;
 
case '2':{
    s+=integrals(a,b,n,f,trap);
    }
    break;
 
case '3':{
    s+=integrals(a,b,n,f,Simpson);
    }
    break;
 
}
cout<<s;
getch();
}

#include "stdafx.h"
#include "iostream"
#include "cmath"
#include "conio.h"
#include "Head1.h"
#include "stdio.h"
#include "stdlib.h"
 
 
using namespace std;
 
 
double f(double x){
    double y=sqrt(1-x*x)*4;
    return (y);
}
 
double rect(double a, double b, Tpf pf){
    double s=(b-a)*pf((a+b)/2);
    return (s);
}
 
double trap(double a, double b, Tpf pf){
    double s=(b-a)/2*(pf(a)+pf(b));
    return (s);
}
 
double Simpson(double a, double b, Tpf pf){
    double s=(b-a)/6*(pf(a)+4*pf((a+b)/2)+pf(b));
    return (s);
}
 
double integrals(double a, double b, int n, Tpf pf, Tpmethod pmethod){
    double h=(b-a)/n;
    double s=0;
    for (int i=0; i<n; i++){
        double l=a+h*i;
        double r=l+h;
        s+=pmethod(l,r,pf);
    }
    return s;
}

#pragma once
#include "cmath"
typedef double(*Tpf)(double);
double f(double x);
typedef double(*Tpmethod)(double, double, Tpf);
typedef double (*integ)(double, double, int, Tpf, Tpmethod);
double rect(double a, double b, Tpf);
double trap(double a, double b, Tpf pf);
double Simpson(double a, double b, Tpf pf);
double integrals(double a, double b, int n, Tpf pf, Tpmethod pmethod);

case 1:
.....
case 2:
.....
case 3:
.....