Bjarne Stroustrup的P：PP Chapter 4 Drill

我刚刚开始学习 c++ ，我正在自学Bjarne Stroustup的p:P& p 。

我在第4章练习。

我遇到的问题似乎与程序的顺序有关。如果我在向量前面添加另一个右花括号来关闭while语句，我将得到max_val和min_val的正确输出。然而，通过添加大括号，即使我想让sum增加双命名数，双命名sum仍然为零。

如果我按照现在编写的方式编译程序(不添加额外的花括号)，我会得到min_val和max_val的错误输出，但sum的正确输出。

同样，正如你在程序底部看到的，这一行:cout << " values were entered." << 'n';不完整。我想打印出输入的总价值，但由于沮丧和需要帮助而使其不完整。我是一个编程新手，任何有建设性的批评，无论多么刺耳，我都将感激不尽。

#include "std_lib_facilities.h"
int main()
{
    double value = 0;
    double max_val = 0;
    double min_val = 0;
    string unit =" ";
    double sum = 0;
    cout << "Enter some numbers, followed by a unit of distance (m, cm, ft, inch):" << 'n';
    while (cin >> value >> unit){
        //determines entered value as max/min/both/neither
        if (min_val == 0 && value > max_val){                       // first number entered is both largest and smallest
            max_val = value;
            min_val = value;
            cout << value << " metres is both the smallest and largest so far" << 'n';
        }
        else if (value < min_val){// smallest number min_val = value;
            cout << min_val << " metres is the smallest so far." << 'n';
        }
        else if (value > max_val){// largest number max_val = value;
            cout << max_val << " metres is the largest so far." << 'n';
        }
        else { // number between smallest and largest
            cout << value << " metres is neither the smallest or largest." << 'n';    }
        //convert entered unit to metres
        if (unit == "m"){
           value = value;
        }
        else if (unit == "cm"){//converts cm to metres
           value = value/100;
        }
        else if (unit == "ft"){//converts ft to metres
           value = value/3.28084;
        }
        else if (unit == "inch"){//converts inch to metres
            value = value/39.3701;
        }
        else{
            cout << "I dont know the unit " << unit << ".";
    }
    vector <double> numbers; //reads input into vector
    double number = 0;
    while (cin >> number) numbers.push_back(number);
    for (double number: numbers) sum += number;
    cout << "The largest value entered was: " << max_val << "." << 'n';
    cout << "The smallest value entered was: " << min_val << "." << 'n';
    cout << "The sum of the numbers entered is: " << sum << "metres" <<'n';
    cout << " values were entered." << 'n';
    keep_window_open("~");
return 0;
}