2.6.3 编写自己的头文件

编写头文件，命名为Sales_data.h，并且编译

#pragma once
#ifndef SALES_DATA_H
#define SALES_DATA_H
#include <string>
struct Sales_data {
	std::string bookNo;
	unsigned units_sold = 0;
	double revenue = 0.0;
};
#endif

练习1.21
与2.6.2不同的是没有在文件内定义类，而是在头文件中定义了，其他代码一样

#include <iostream>
using namespace std;
#include "Sales_data.h"

int main() {

    Sales_data data1, data2;
    //读入data1和data2的代码
    double price = 0.0; //书的单价
    //读入第一本交易：ISBN,销售数量，单价
    cin >> data1.bookNo >> data1.units_sold >> price;
    //计算销售收入
    data1.revenue = data1.units_sold * price;
    //读入第二本交易：ISBN,销售数量，单价
    cin >> data2.bookNo >> data2.units_sold >> price;
    //计算销售收入
    data2.revenue = data2.units_sold * price;

    //检查两笔交易涉及的ISBN号是否相同
    if (data1.bookNo == data2.bookNo) {
        unsigned totalCnt = data1.units_sold + data2.units_sold;
        double totalRevenue = data1.revenue + data2.revenue;
        //输出 ISBN,总销售量，总销售额，平均价格
        cout << data1.bookNo << " " << totalCnt << " " << totalRevenue << " ";
        if (totalCnt != 0) {
            cout << totalRevenue / totalCnt << endl;
        }
        else {
            cout << "No sales" << endl;
        }
    }
    else { //两笔交易的ISBN 不一样
        cerr << "Data must refer to the same ISBN" << endl;
        return -1;
    }
    return 0;
}

练习1.22

#include <iostream>
using namespace std;
#include "Sales_data.h"

int main() {

    Sales_data data1;
    double price = 0.0;
    cin >> data1.bookNo >> data1.units_sold >> price;
    data1.revenue = data1.units_sold * price;

    Sales_data data2;
    while (cin >> data2.bookNo >> data2.units_sold >> price) {
        data2.revenue = data2.units_sold * price;
        if (data1.bookNo == data2.bookNo) {
            unsigned totalCnt = data1.units_sold + data2.units_sold;
            double totalRevenue = data1.revenue + data2.revenue;
            cout << "Result " << data1.bookNo << " " << totalCnt << " " << totalRevenue << " ";
            data1.revenue = totalRevenue; //把总收入和总销售数量重新赋值给data1，用于累加
            data1.units_sold = totalCnt;
            if (totalCnt != 0) {
                cout << totalRevenue / totalCnt << endl;
            }
            else {
                cout << "No sales" << endl;
            }
        }
        else {
            cerr << "Data must refer to the same ISBN" << endl;
            return -1;
        }
    }

}

#include <iostream>
using namespace std;
#include "Sales_data.h"

int main() {

    Sales_data data1;//保存下一条交易记录的变量
    double price = 0.0;
    //读入第一条交易记录，并确保有数据可以处理
    if (cin >> data1.bookNo >> data1.units_sold >> price)
    {
        data1.revenue = data1.units_sold * price;
        int a = 1; //保存次数的变量
        Sales_data data2;
        while (cin >> data2.bookNo >> data2.units_sold >> price) {
            //如果我们在处理相同的书
            data1.revenue = data1.units_sold * price;
            if (data1.bookNo == data2.bookNo)
                a = a + 1; //更新总次数
            else {
                //打印前一笔交易的次数
                cout << a << endl;
                data1 = data2; //data1现在表示下一本书
                a = 1; //开始计算下一笔交易的次数
            }
        }
        cout << a << endl; //打印最后一笔交易的结果
    }
    else {
        //没有输入
        cerr << "No data?" << endl;
        return -1;
    }
    return 0;

}

#include <iostream>
using namespace std;
#include "Sales_data.h"

int main() {
    Sales_data total;//保存下一条交易记录的变量
    double price = 0.0;
    //读入第一条交易记录，并确保有数据可以处理
    if (cin >> total.bookNo >> total.units_sold >> price)
    {
        total.revenue = total.units_sold * price;
        Sales_data trans;

        while (cin >> trans.bookNo >> trans.units_sold >> price) {
            //如果我们在处理相同的书
            trans.revenue = trans.units_sold * price;
            if (total.bookNo == trans.bookNo) {
                total.revenue = total.revenue + trans.revenue;
                total.units_sold = total.units_sold + trans.units_sold;
            }
            else {
                //打印前一笔交易的次数
                cout << "Result is " << total.bookNo << " " << total.units_sold << " " << total.revenue << endl;
                total = trans;

            }
        }
        cout << "Result is  " << total.bookNo << " " << total.units_sold << " " << total.revenue << endl; //打印最后一笔交易的结果

    }
    else {
        //没有输入
        cerr << "No data?" << endl;
        return -1;
    }
    return 0;

}