Jeg tror vi skal se NewItem.h for at kunne hjælpe.
Jeg omdøbte filen til NewItem.h - men man må godt
distribuere den egentlige kode, bare man ved hvor
den kommer fra.
Dette er taget fra:
(C++ Primer 4th. Edition - Exercise 1.26)
Okay, her er den egentlige kode:
#include <iostream>
#include "Sales_item.h"
int main()
{
// declare variables to hold running sum and data for the next record
Sales_item total, trans;
// is there data to process?
if (std::cin >> total) {
// if so, read the transaction records
while (std::cin >> trans)
if (total.same_isbn(trans))
// match: update the running total
total = total + trans;
else {
// no match: print & assign to total
std::cout << total << std::endl;
total = trans;
}
// remember to print last record
std::cout << total << std::endl;
} else {
// no input!, warn the user
std::cout << "No data?!" << std::endl;
return -1; // indicate failure
}
return 0;
}Her er header filen:
Sales_item.h
#ifndef SALESITEM_H
#define SALESITEM_H
// Definition of Sales_item class and related functions goes here
#include <iostream>
#include <string>
class Sales_item {
friend bool operator==(const Sales_item&, const Sales_item&);
// other members as before
public:
// added constructors to initialize from a string or an istream
Sales_item(const std::string &book):
isbn(book), units_sold(0), revenue(0.0) { }
Sales_item(std::istream &is) { is >> *this; }
friend std::istream& operator>>(std::istream&, Sales_item&);
friend std::ostream& operator<<(std::ostream&, const Sales_item&);
public:
// operations on Sales_item objects
// member binary operator: left-hand operand bound to implicit this pointer
Sales_item& operator+=(const Sales_item&);
// other members as before
public:
// operations on Sales_item objects
double avg_price() const;
bool same_isbn(const Sales_item &rhs) const
{ return isbn == rhs.isbn; }
// default constructor needed to initialize members of built-in type
Sales_item(): units_sold(0), revenue(0.0) { }
// private members as before
private:
std::string isbn;
unsigned units_sold;
double revenue;
};
// nonmember binary operator: must declare a parameter for each operand
Sales_item operator+(const Sales_item&, const Sales_item&);
inline bool
operator==(const Sales_item &lhs, const Sales_item &rhs)
{
// must be made a friend of Sales_item
return lhs.units_sold == rhs.units_sold &&
lhs.revenue == rhs.revenue &&
lhs.same_isbn(rhs);
}
inline bool
operator!=(const Sales_item &lhs, const Sales_item &rhs)
{
return !(lhs == rhs); // != defined in terms of operator==
}
using std::istream; using std::ostream;
// assumes that both objects refer to the same isbn
inline
Sales_item& Sales_item::operator+=(const Sales_item& rhs)
{
units_sold += rhs.units_sold;
revenue += rhs.revenue;
return *this;
}
// assumes that both objects refer to the same isbn
inline
Sales_item
operator+(const Sales_item& lhs, const Sales_item& rhs)
{
Sales_item ret(lhs); // copy lhs into a local object that we'll return
ret += rhs; // add in the contents of rhs
return ret; // return ret by value
}
inline
istream&
operator>>(istream& in, Sales_item& s)
{
double price;
in >> s.isbn >> s.units_sold >> price;
// check that the inputs succeeded
if (in)
s.revenue = s.units_sold * price;
else
s = Sales_item(); // input failed: reset object to default state
return in;
}
inline
ostream&
operator<<(ostream& out, const Sales_item& s)
{
out << s.isbn << "\\t" << s.units_sold << "\\t"
<< s.revenue << "\\t" << s.avg_price();
return out;
}
inline
double Sales_item::avg_price() const
{
if (units_sold)
return revenue/units_sold;
else
return 0;
}
#endif
Indlæg senest redigeret d. 21.10.2007 20:53 af Bruger #9738