c++ - 无法弄清楚如何循环计算单个学生的总数

Question

我遇到了这个程序的问题。我需要它来询问用户 ID，然后询问书籍代码，然后询问书籍的费用。个人可以输入未知数量的书籍。程序需要计算每个学生的书本总数，然后询问另一个做同样事情的学生。然后程序必须显示总数和书籍总数。我似乎无法弄清楚使用什么来跟踪个别学生的条目。我将能够从我正在阅读的有关数组的内容中做到这一点。但我们还没有到那个地步。教授希望我们用循环来做这件事。我很迷茫，任何帮助都会很棒。

#include <iostream>
#include <iomanip>

using namespace std;
int main ()
{
    //Declare Variables.
    int student_id;
    char book_code;
    float book_cost;
    float tax_amount;
    float book_subtotal;
    const int SENTINEL = -9999;
    const double TAX = .07;
    float total_book_cost;
    int number_books;
    int total_books_sold;
    double grand_total;

    //Set Variables to Zero.
    number_books = 0;
    total_book_cost = 0.00;
    grand_total = 0.00;

    //Set Decimal to two places.
    cout << fixed << showpoint;
    cout << setprecision(2);

    //Input Data
    cout<<"Please enter your Student ID, then press enter."<<endl;
    cin>>student_id;
    while (student_id != SENTINEL){
        cout<<"Please enter your Book Code, then press enter."<<endl;
        cin>>book_code;
        cout<<"Please enter the cost of the book, then press enter."<<endl;
        cout<<"$"; cin>>book_cost;
        tax_amount = book_cost * TAX;
        book_subtotal = book_cost + tax_amount;
        total_book_cost += book_subtotal;
        number_books++;
        cout<<"\tStudent Textbook Purchases Report"<<endl;
        cout<<"********************************************"<<endl;
        cout<<"Student"<<"\tBook"<<"\tBook"<<"\tTax"<<"\tBook"<<endl;
        cout<<"Id"<<"\tCode"<<"\tCost"<<"\tAmount"<<"\tSubtotal"<<endl;
        cout<<"--------------------------------------------"<<endl;
        cout<<student_id<<setw(5)<<book_code<<setw(8)<<"$"<<book_cost<<
        setw(3)<<"$"<<tax_amount<<setw(4)<<"$"<<book_subtotal<<endl;
        cout<<endl;
        cout<<"Total number of books purchased:"<<setw(8)<<number_books<<endl;
        cout<<"Total books cost including tax:"<<setw(9)<<"$"<<total_book_cost<<endl;
        cout<<"Please enter your Student ID, then press enter."<<endl;
        cin>>student_id;
    }
    grand_total += total_book_cost;
    total_books_sold += number_books;
    cout<<"**************************************************"<<endl;
    cout<<"Grand Totals:"<<endl;
    cout<<"Total number of students who purchased books:"<<endl;
    cout<<"Total number of books sold:"<<endl;
    cout<<"Total cost of all books and taxes:"<<setw(9)<<"$"<<grand_total<<endl;

    //Can put grand totals here

    system("Pause");
    return 0;
}

Answer 1

您可以像这样使用循环：

#include <iostream>
#include <iomanip>

using namespace std;
int main ()
{

    //Set Decimal to two places.
    cout << fixed << showpoint;
    cout << setprecision(2);


    int total_books_sold = 0;
    double grand_total = 0.0;

    const int SENTINEL = -9999;
    int     student_id = SENTINEL;
    //Input Data
    cout<<"Please enter your Student ID, then press enter."<<endl;
    cin>>student_id;

    while (student_id != SENTINEL){

        double  total_book_cost = 0.0;
        int     number_books = 0;
        char    book_code = '\0';
        while (true) 
        {
            cout<<"Please enter your Book Code, then press enter."<<endl;
            cin>>book_code;

            if (book_code == 'x')
                break;

            float   book_cost;
            cout<<"Please enter the cost of the book, then press enter."<<endl;
            cout<<"$"; cin>>book_cost;

            const double TAX = .07;
            double tax_amount = book_cost * TAX;
            double book_subtotal = book_cost + tax_amount;

            total_book_cost += book_subtotal; 
            number_books++;

            cout<<"\tStudent Textbook Purchases Report"<<endl;
            cout<<"********************************************"<<endl;
            cout<<"Student"<<"\tBook"<<"\tBook"<<"\tTax"<<"\tBook"<<endl;
            cout<<"Id"<<"\tCode"<<"\tCost"<<"\tAmount"<<"\tSubtotal"<<endl;
            cout<<"--------------------------------------------"<<endl;
            cout<<student_id<<setw(5)<<book_code<<setw(8)<<"$"<<book_cost<<
                setw(3)<<"$"<<tax_amount<<setw(4)<<"$"<<book_subtotal<<endl;
            cout<<endl;

        };


        grand_total += total_book_cost;
        total_books_sold += number_books;

        cout<<"Total number of books purchased:"<<setw(8)<<number_books<<endl;
        cout<<"Total books cost including tax:"<<setw(9)<<"$"<<total_book_cost<<endl;
        cout<<"Please enter your Student ID, then press enter."<<endl;
        cin>>student_id;
    }


    cout<<"**************************************************"<<endl;
    cout<<"Grand Totals:"<<endl;
    cout<<"Total number of students who purchased books:"<<endl;
    cout<<"Total number of books sold:"<<endl;
    cout<<"Total cost of all books and taxes:"<<setw(9)<<"$"<<grand_total<<endl;

    //Can put grand totals here

    system("Pause");
    return 0;
}