C++ Primer第一章！

#include "stdafx.h"
#include<iostream>

using namespace std;

class Sum_atob
{
public:
    Sum_atob() = default;
    Sum_atob(const int &a, const int &b) :a(a), b(b) {};
    int getsum()
    {
        int sum=0;
        if (a > b)
        {
            int tmp = a;
            a = b;
            b = tmp;
        }
        for (int i = a; i <= b; ++i)
        {
            sum += i;
        }
        return sum;
    };
private:
    int a = 0;
    int b = 0;
};

int main()
{

        cout << "hello world!" << endl;  //标准输出
    cerr << "wrong!"<<endl;          //标准错误
    clog << "runing"<<endl;          //log信息
    cin.ignore();                            //标准输入

    std::cout << "Enter two numbers:" << endl;
    int v1=0, v2(0);              //函数内内置类型要初始化，否则会导致未定义。
    cin >> v1 >> v2;
    cout << "The sum of " << v1 << " and " << v2 << " is " << v1 +v2 << endl;;
    cin.ignore();               //为什么此处失效了？

    int sum = 0, val = 1;
    while (val <= 10)
    {
        sum += val;
        ++val;
    }
    cout << "Sum of 1 to 10 inclusive is " << sum << endl;
    cin.ignore();

    int sum_for = 0;
    for (int val_for = 1; val_for <= 10; ++val_for)
    {
        sum_for += val_for;
    }
    cout << "Sum of 1 to 10 inclusive is " << sum_for << endl;
    cin.ignore();

    cout <<"Sum of 1 to 10 inclusive is "<< Sum_atob(1, 10).getsum() << endl;//通过类实现1到10累加。

    int sum_no_limit = 0, value = 0;
    while (cin >> value)    //监测输入流的状态，如果有效则保持循环
    {
        sum_no_limit += value;
    }
    cout << "Sum is " << sum_no_limit << endl;
    cin.ignore();

    int currval = 0, val_next = 0;
    if (cin >> currval)
    {
        int cnt = 1;
        while (cin>>val_next)
        {
            if (val_next == currval)
                ++cnt;
            else
            {
                cout << currval << " occurs " << cnt << " times" << endl;
                currval = val_next;
                cnt = 1;
            }
        }
        cout << currval << " occurs " << cnt << " times" << endl;
    }
    cin.ignore();

    return 0;
}

//类型是程序设计的基本概念，不仅定义了数据的内容，也定义了数据的运算方法，例如int类型，为内置类型。
//程序所处理的数据都保存在变量中，而每个变量都有自己的类型。定义形式，int i=0;
//可以在命令行对cpp进行编译(开始-VC工具-x64 Native Tools Command Prompt for VS 2017 Preview-cl /EHsc chapter-1.cpp）
//endl为操纵符，用于结束当前行，并将缓冲区内容刷到设备中。
//std为命名空间，标准库定义的所有名字都在命名空间std中，使用形式std::cout/using namespace std。