primer plus 9--4，新手求教。。。。
#ifndef SALE_H_INCLUDED //头文件
#define SALE_H_INCLUDED

namespace SALES
{
const int QUARTERS=4;
struct Sales
{
double sales[QUARTERS];
double average;
double max;
double min;
};

void setSales(Sales & s,const double ar[],int n);

void setSales(Sales & s);

void showSales(const Sales & s);
}


#endif // SALE_H_INCLUDED

//file1

#include <iostream>
#include "sale.h"
using namespace SALES;
void setSales(Sales & s,const double ar[],int n)
{
using namespace std;
double min=max=ar[0],temp=0;
for(int i=0;i<QUARTERS;i++)
{
if(i<n)
{
s.sales[i]=ar[i];
if(ar[i]>max)
max=ar[i];
else
min=ar[i];
}
else
s.sales[i]=0;
temp+=ar[i];
}
s.max=max;
s.min=min;
s.average=temp/n;
}

void setSales(Sales & s);
{
double min=max=ar[0],temp=0;
for(int i=0;i<QUARTERS;i++)
{
s.sales[i]=ar[i];
if(ar[i]>max)
max=ar[i];
else
min=ar[i];
temp+=ar[i];
}
s.max=max;
s.min=min;
s.average=temp/QUARTERS;
}

void showSales (const Sales & s)
{
using namespace std;
for(int i=0;i<QUARTERS;i++)
cout<<s.sales[i]<<endl;
cout<<"Average= "<<s.average<<endl;
cout<<"Max= "<<s.max<<endl;
cout<<"Min= "<<s.min<<endl;
}

//file2

#include<iostream>
#include "sale.h"

using namespace SALES;
int main()
{
using namespace std;
Sales fir,sec;
const double ar[4]={1,2,3,4};
int n;
cout<<"Enter the count of numbers(1~4): ";
cin>>n;
void setSales(fir,ar,n);
void showSales(fir);
void setSales(sec);
void showSales(sec);

cout<<"\nDone\n";
return 0;
}

file2出问题了，
error: variable or field 'setSales' declared void
error: variable or field 'showSales' declared void
error: variable or field 'setSales' declared void
error: variable or field 'showSales' declared void

不知道怎么解决，求指导啊，刚学C++，希望大神说的稍微详细点，谢谢

[解决办法]
调用的时候是这样的：
setSales(fir,ar,n);
showSales(fir);
setSales(sec);
showSales(sec);