为什么 Sales_Item.h 需要两个 ctrl+Z 而不是一个？

如何解决为什么 Sales_Item.h 需要两个 ctrl+Z 而不是一个？

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: [phone]
*/ 

/* 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？