C++primer Ch1

作者: 晶Sama | 来源:发表于2019-04-17 18:29 被阅读0次

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本章主要工作是编写了一个书店程序，关于语句块，main函数等非常基础的知识不会再提。我使用的IDE是code:blocks，由于VS2010不支持C++11就没有用VS。书中的命令行运行程序即在cmd中运行，大家可以自己尝试，本文不作示范。

知识点1

首先要认识的iostream库，库内包含两个基础类型istream（输入流）和ostream（输出流）。
标准库定义4个IO对象，cin（标准输入）, cout（标准输出）, cerr（输出警告或错误）, clog（输出程序运行时的信息），>> 输入运算符，<<输出运算符，分别对流进行输入输出操作。
没有using namespace std;时，使用命名空间内的名字必须用std::（如std::cout）

习题1

1.1 （略）
1.2 运行后显示process returned -1
1.3

#include<iostream>
int main()
{
    std::cout <<" Hello, world." << std::endl;
    return 0;
}

1.4

#include<iostream>
int main()
{
    std::cout << "Enter two numbers:" << std::endl;
    int v1 = 0, v2 = 0;
    std::cin >> v1 >> v2;
    std::cout << "The product of " << v1 << " and " << v2
              << "is " << v1 * v2 <<std::endl;
    return 0;
}

1.5

#include<iostream>
int main()
{
    std::cout << "Enter two numbers:" ;
    std::cout << std::endl;
    int v1 = 0, v2 = 0;
    std::cin >> v1 >> v2;
    std::cout << "The sum of " ;
    std::cout << v1 ;
    std::cout << " and ";
    std::cout << v2 ;
    std::cout << " is " ;
    std::cout << v1 + v2 ;
    std::cout << std::endl;
    return 0;
}

1.6 不合法，去掉中间的分号，后者后两句最前面加std::cout

知识点2

注释，同C //单行 /* /多行，注意：注释是不能嵌套的

习题2

1.7 自己试一下，应该都会有这句
warning: "/" within comment [-Wcomment]|
1.8 第一个和第二个合法，后两个均不合法，第三个最后加一个 " 就可以打印/，第四个是<<后面全被注释掉

知识点3

while循环：while(condition){ statement }
for循环：for(初始化计数变量;判断条件;++)，通常都用前++形式防止出错
读取不定量数据常用while(cin >> val)，输入ctrl+z可终止输入
if语句，和C中if基本相同

习题3

1.9

#include<iostream>

int main()
{
    int sum = 0, val = 50;
    while(val <= 100)
    {
        sum += val;
        val++;
    }
    std::cout << "The sum of 50 to 100 is " << sum
              << std::endl;

    return 0;
}

1.10

#include<iostream>

int main()
{
    int i = 10;
    while(i >= 0)
    {
        std::cout << i-- << " ";
    }

    return 0;
}

1.11

#include<iostream>

int main()
{
    int i, j;
    std::cout << "Enter two numbers:" << std::endl;
    std::cin >> i >> j;
    std::cout << "The numbers between " << i << " and "
              << j << "is ";
    while(i < j)
    {
        std::cout << i << " ";
        i++;
    }
    while(i > j)
    {
        std::cout << j << " ";
        j++;
    }
    return 0;

}

1.12 从-100一直加到100 sum的终值是0
1.13

#include<iostream>
int main()
{
    //50到100相加
    int sum = 0;
    int v1, v2;

    for(int i = 50; i <= 100; ++i)
        sum += i;
    std::cout << "Sum of 50 to 100 inclusive is "
              << sum << std::endl;
    //输出10到0
    for(int i = 10; i >= 0; i--)
        std::cout << i << " ";
    std::cout << std::endl;
    //输出两个整数范围内所有整数
    std::cout << "Enter two numbers: " << std::endl;
    std::cin >> v1 >> v2;
    for(v1; v1 < v2; v1++)
        std::cout << v1 << " ";
    for(v2; v2 < v1; v2++ )
        std::cout << v2 << " ";

    return 0;
}

1.14 for循环指定次数，while循环可不固定次数
1.15 14页指出了语法错误，声明错误，类型错误。
1.16

#include<iostream>
int main()
{
    int sum = 0, value = 0;
    while(std::cin >> value)
        sum += value;
    std::cout << "Sum is: " << sum << std::endl;

    return 0;
}

1.17 输出结果为输入的同样的数出现了多少次，例如都是1的话
1 occurs 7 times
1.18

#include<iostream>

int main()
{
    int currVal = 0, val = 0;
    if (std::cin >> currVal){
        int cnt = 1;
        while (std::cin >> val){
            if (val == currVal)
                ++cnt;
            else{
                std::cout << currVal << " occurs "
                          << cnt << "times" <<std::endl;
                currVal = val;
                cnt = 1;

            }
        }//while
        std::cout << currVal << " occurs "
                  <<cnt << " times " << std::endl;
    }//if

    return 0;
}

1.19

#include<iostream>

int main()
{
    int i, j;
    std::cout << "Enter two numbers:" << std::endl;
    std::cin >> i >> j;
    std::cout << "The numbers between " << i << " and "
              << j << "is ";
    if (i < j){

        while(i <= j)
        {
            std::cout << i << " ";
            i++;
        }
    }
    else{
        while(i >= j)
        {
            std::cout << j << " ";
            j++;
        }
    }
    return 0;

}

知识点4

类，定义了一个数据结构和与其关联的一组操作。类类型是面向对象程序语言一个的特征
成员函数（类中的函数），通过点运算符访问。

习题4

Sales_item.h


#ifndef SALESITEM_H
#define SALESITEM_H
#include <iostream>
#include <string>
class Sales_item
{
public:
    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:
    Sales_item & operator+=(const Sales_item&);
public:
    double avg_price() const;
    bool same_isbn(const Sales_item &rhs)const
    {
        return isbn == rhs.isbn;
    }
    Sales_item():units_sold(0),revenue(0.0){}
public:
    std::string isbn;
    unsigned units_sold;
    double revenue;
};

using std::istream;
using std::ostream;
Sales_item operator+(const Sales_item &,const Sales_item &);
inline bool operator==(const Sales_item &lhs,const Sales_item &rhs)
{
    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);
}

inline Sales_item & Sales_item::operator +=(const Sales_item &rhs)
{
    units_sold += rhs.units_sold;
    revenue += rhs.revenue;
    return *this;
}
inline Sales_item operator+(const Sales_item &lhs,const Sales_item &rhs)
{
    Sales_item ret(lhs);
    ret += rhs;
    return ret;
}
inline istream& operator>>(istream &in,Sales_item &s)
{
    double price;
    in >> s.isbn >> s.units_sold >> price;
    if(in)
        s.revenue = s.units_sold * price;
    else
        s = Sales_item();
    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

1.20

#include<iostream>
#include"Sales_item.h"
int main()
{
    Sales_item book;
    while(std::cin >> book){
            std::cout << book << std::endl;
    }


    return 0;
}

1.21

#include<stdio.h>
#include"Sales_item.h"

int main()
{
    Sales_item book1, book2;
    std::cin >> book1 >> book2;
    if(book1.isbn == book2.isbn)
        std::cout << book1 + book2 << std::endl;
    else
        std::cout << "False input!";

    return 0;
}

1.22

#include<stdio.h>
#include"Sales_item.h"
int main()
{
    Sales_item book, total;
    std::cin >> total;
    while(std::cin >> book && (total.isbn == book.isbn))
    {
        total += book;
    }                                                   //不太懂两次ctrl+z才可退出
    std::cout << total << std::endl;

    return 0;
}

1.23，24

#include<stdio.h>
#include"Sales_item.h"
int main()
{
    Sales_item currbook, book;
    if (std::cin >> currbook){
        int cnt = 1;
        while(std::cin >> book){
            if (currbook.isbn == book.isbn)
                cnt++;
            else{
                std::cout << currbook.isbn << " has sold " <<cnt
                          << "times" << std::endl;
                currbook = book;
                cnt = 1;
            }
        }
        std::cout << currbook.isbn << " has sold " <<cnt
                          << "times" << std::endl;
    }

    return 0;
}

1.25

#include<iostream>
#include"Sales_item.h"
int main()
{
    Sales_item total;

    if(std::cin >> total){
        Sales_item trans;
        while(std::cin >> trans){
            if(total.isbn == trans.isbn)
                total += trans;
            else{
                std::cout << total << std::endl;
                total = trans;
            }
        }
        std::cout << total << std::endl;
    }
    else{
            std::cerr << "No data!" << std::endl;
            return -1;
    }

    return 0;
}

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