问题描述
在 C++ Primer 5th Edition book 中,我在 1.4.4 章节中看到了这一点
#include <iostream>
int main()
{
// currVal is the number we're counting; we'll read new values into val
int currVal = 0,val = 0;
// read first number and ensure that we have data to process
if (std::cin >> currVal)
{
int cnt = 1; // store the count for the current value we're processing
while (std::cin >> val)
{ // read the remaining numbers
if (val == currVal) // if the values are the same
++cnt; // add 1 to cnt
else
{ // otherwise,print the count for the prevIoUs value
std::cout << currVal << " occurs "
<< cnt << " times" << std::endl;
currVal = val; // remember the new value
cnt = 1; // reset the counter
}
} // while loop ends here
// remember to print the count for the last value in the file
std::cout << currVal << " occurs "
<< cnt << " times" << std::endl;
} // outermost if statement ends here
return 0;
}
他们说如果我输入这个 42 42 42 42 42 55 55 62 100 100 100
(但我必须使用一个行尾或 ctrl+Z)
它会打印:
42 occurs 5 times
55 occurs 2 times
62 occurs 1 times
100 occurs 3 times
如果我输入它,它会打印出来。但是,如果我使用 enter 而不是空格输入数字,则会在输入所有数字之前给出一些结果:(
但是当我使用 1.6 章中的这段代码时
#include <iostream>
#include "Sales_item.h"
int main()
{
Sales_item total; // variable to hold data for the next transaction
// read the first transaction and ensure that there are data to process
if (std::cin >> total)
{
Sales_item trans; // variable to hold the running sum
// read and process the remaining transactions
while (std::cin >> trans)
{
// if we're still processing the same book
if (total.isbn() == trans.isbn())
total += trans; // update the running total
else
{
// print results for the prevIoUs book
std::cout << total << std::endl;
total = trans; // total Now refers to the next book
}
}
std::cout << total << std::endl; // print the last transaction
}
else
{
// no input! warn the user
std::cerr << "No data?!" << std::endl;
return -1; // indicate failure
}
return 0;
}
这次我不得不用ctrl+Z两次。顺便说一句,我无法从 C++ Primer 5th Edition 链接中获取 Sales_Item.h 类。所以我在谷歌搜索了 Sales_Item.h 并从 Github.com 下载了一个。 Sales_Item.h 类的代码为:
/*
* This file contains code from "C++ Primer,Fifth Edition",by Stanley B.
* Lippman,Josee Lajoie,and Barbara E. Moo,and is covered under the
* copyright and warranty notices given in that book:
*
* "copyright (c) 2013 by Objectwrite,Inc.,and Barbara E. Moo."
*
*
* "The authors and publisher have taken care in the preparation of this book,* but make no expressed or implied warranty of any kind and assume no
* responsibility for errors or omissions. No liability is assumed for
* incidental or consequential damages in connection with or arising out of the
* use of the information or programs contained herein."
*
* Permission is granted for this code to be used for educational purposes in
* association with the book,given proper citation if and when posted or
* reproduced.Any commercial use of this code requires the explicit written
* permission of the publisher,Addison-Wesley Professional,a division of
* Pearson Education,Inc. Send your request for permission,stating clearly
* what code you would like to use,and in what specific way,to the following
* address:
*
* Pearson Education,Inc.
* Rights and Permissions Department
* One Lake Street
* Upper Saddle River,NJ 07458
* Fax: (201) 236-3290
*/
/* This file defines the Sales_item class used in chapter 1.
* The code used in this file will be explained in
* Chapter 7 (Classes) and Chapter 14 (Overloaded Operators)
* Readers shouldn't try to understand the code in this file
* until they have read those chapters.
*/
#ifndef SALESITEM_H
// we're here only if SALESITEM_H has not yet been defined
#define SALESITEM_H
// DeFinition of Sales_item class and related functions goes here
#include <iostream>
#include <string>
class Sales_item {
// these declarations are explained section 7.2.1,p. 270
// and in chapter 14,pages 557,558,561
friend std::istream& operator>>(std::istream&,Sales_item&);
friend std::ostream& operator<<(std::ostream&,const Sales_item&);
friend bool operator<(const Sales_item&,const Sales_item&);
friend bool
operator==(const Sales_item&,const Sales_item&);
public:
// constructors are explained in section 7.1.4,pages 262 - 265
// default constructor needed to initialize members of built-in type
Sales_item() = default;
Sales_item(const std::string &book): bookNo(book) { }
Sales_item(std::istream &is) { is >> *this; }
public:
// operations on Sales_item objects
// member binary operator: left-hand operand bound to implicit this pointer
Sales_item& operator+=(const Sales_item&);
// operations on Sales_item objects
std::string isbn() const { return bookNo; }
double avg_price() const;
// private members as before
private:
std::string bookNo; // implicitly initialized to the empty string
unsigned units_sold = 0; // explicitly initialized
double revenue = 0.0;
};
// used in chapter 10
inline
bool compareIsbn(const Sales_item &lhs,const Sales_item &rhs)
{ return lhs.isbn() == rhs.isbn(); }
// 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.isbn() == rhs.isbn();
}
inline bool
operator!=(const Sales_item &lhs,const Sales_item &rhs)
{
return !(lhs == rhs); // != defined in terms of operator==
}
// assumes that both objects refer to the same ISBN
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
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
}
std::istream&
operator>>(std::istream& in,Sales_item& s)
{
double price;
in >> s.bookNo >> 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;
}
std::ostream&
operator<<(std::ostream& out,const Sales_item& s)
{
out << s.isbn() << " " << s.units_sold << " "
<< s.revenue << " " << s.avg_price();
return out;
}
double Sales_item::avg_price() const
{
if (units_sold)
return revenue/units_sold;
else
return 0;
}
#endif
也许我需要按 ctrl+Z 两次,因为 sales_item.h 文件是 bot 真实的。如果是真的,那么我需要真正的 sales_item.h 文件 :)。但我的主要问题是我是否需要按 ctrl+Z 两次,因为这是 Sales_item 类或任何编码错误?
解决方法
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