结构，数组和函数C ++

Question

我完全坚持这个任务。 我首先在int main（）中写了所有内容，没有任何问题。 这一切都很可爱！ 不幸的是，我们的教练希望它分成多个功能（每个功能少于35行）。 我已将其分解，如下所示，但不幸的是，我的知识（和谷歌没有太多帮助）的功能和传递/参考通过它们并不是那么高。 我的程序现在根本不起作用。 所有的“书籍”都会出错，所以我不确定我是否正在不正确地传递结构或数组。 请帮忙！

原始的txt文件如下：

number of books
title
author
price
title
author
price

码：

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>

using namespace std;

void setStruct() {

    struct bookTable {
        string title;
        string author;
        double price;
    };
}

void setArray(int &arraySize, struct bookTable *Book[]) {

    ifstream infile;
    int bookCounter = 0;

    infile.open("books2.txt");

    if (!infile) {
        cout << "Unable to open Books.txt" << endl;
    }

    infile >> arraySize;
    infile.ignore(100, '\n');

    bookTable *Book = new bookTable[arraySize];

    infile.close();
}

void readFile(struct bookTable *Book[]) {

    ifstream infile;
    int bookCounter = 0;

    infile.open("books2.txt");

    for (int i = 0; getline(infile, Book[i].title); i++) {

        getline(infile, Book[i].author, '\n');
        infile >> Book[i].price;
        infile.ignore(100, '\n');

        bookCounter++;
    }

    infile.close();
}

void displayMenu(struct bookTable *Book[]) {
    int menuChoice = 0, bookCounter = 0;
    string findTitle;

    do { cout << "\n===== Bookstore App =====" << endl; 
    cout << "1. Print Books" << endl; 
    cout << "2. Change Price" << endl;
    cout << "3. Quit" << endl; 
    cout << "\nEnter Choice: ";
        cin >> menuChoice;
        if (menuChoice == 1) {
            for (int i = 0; i < bookCounter; i++) {
                cout << "===== BOOK =====" << endl;
                cout << "Title: " << Book[i].title << endl;
                cout << "Author: " << Book[i].author << endl;
                cout << "Price: " << fixed << setprecision(2) << Book[i].price << endl; } }
        else if (menuChoice == 2) { cin.ignore(100, '\n');
            cout << "What is the title of the book? ";
            getline(cin, findTitle, '\n');
            for (int i = 0; i < bookCounter; i++) {
                if (findTitle == Book[i].title) {
                    cout << "Enter New Price: " << endl;
                    cin >> Book[i].price;
                }
                else if (findTitle != Book[i].title) {
                    cout << "Unable to find Book" << endl;
                }}}

        else if (menuChoice < 1 || menuChoice > 3) {

            cout << "Invalid Entry. Please enter 1, 2, or 3 from the options menu." << endl;
        }   } while (menuChoice != 3);
}

void writeFile(int arraySize, struct bookTable *Book[]) {

    ofstream outfile;
    int bookCounter = 0;

    outfile.open("sale2.txt");

    outfile << arraySize << endl;

    for (int i = 0; i < bookCounter; i++) {

        outfile << Book[i].title << endl;
        outfile << Book[i].author << endl;
        outfile << fixed << setprecision(2) << Book[i].price << endl;
    }

    outfile.close();

    delete[] Book;

}

int main() {

    setStruct();
    setArray();
    readFile();
    displayMenu();
    writeFile();

    cout << "\nSale2.txt has been created." << endl;

    return 0;
} 

Answer 1

我没有编译或运行它，但希望它能让你开始朝着正确的方向前进：

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>

using namespace std;

// This declares "struct bookTable"
// You need to actually define a variable of this type later in your program
struct bookTable {
    string title;
    string author;
    double price;
};

bookTable * setArray(int &arraySize, struct bookTable *Book[]) {

    ifstream infile;
    int bookCounter = 0;

    infile.open("books2.txt");

    if (!infile) {
        cout << "Unable to open Books.txt" << endl;
    }

    infile >> arraySize;
    infile.ignore(100, '\n');

    bookTable *Book = new bookTable[arraySize];

    infile.close();

    // This returns an empty array of bookTable[]
    return Book;
}

void readFile(struct bookTable *Book) {

    ifstream infile;
    int bookCounter = 0;

    infile.open("books2.txt");

    for (int i = 0; getline(infile, Book[i].title); i++) {

        getline(infile, Book[i].author, '\n');
        infile >> Book[i].price;
        infile.ignore(100, '\n');

        bookCounter++;
    }

    infile.close();
}

void displayMenu(struct bookTable *Book[]) {
    int menuChoice = 0, bookCounter = 0;
    string findTitle;

    do { cout << "\n===== Bookstore App =====" << endl; 
    cout << "1. Print Books" << endl; 
    cout << "2. Change Price" << endl;
    cout << "3. Quit" << endl; 
    cout << "\nEnter Choice: ";
        cin >> menuChoice;
        if (menuChoice == 1) {
            for (int i = 0; i < bookCounter; i++) {
                cout << "===== BOOK =====" << endl;
                cout << "Title: " << Book[i].title << endl;
                cout << "Author: " << Book[i].author << endl;
                cout << "Price: " << fixed << setprecision(2) << Book[i].price << endl; } }
        else if (menuChoice == 2) { cin.ignore(100, '\n');
            cout << "What is the title of the book? ";
            getline(cin, findTitle, '\n');
            for (int i = 0; i < bookCounter; i++) {
                if (findTitle == Book[i].title) {
                    cout << "Enter New Price: " << endl;
                    cin >> Book[i].price;
                }
                else if (findTitle != Book[i].title) {
                    cout << "Unable to find Book" << endl;
                }}}

        else if (menuChoice < 1 || menuChoice > 3) {

            cout << "Invalid Entry. Please enter 1, 2, or 3 from the options menu." << endl;
        }   } while (menuChoice != 3);
}

//  !!! DON'T UNCOMMENT THIS UNTIL YOU FIGURE OUT HOW TO PRESERVE "arraySize" !!!
//      Suggestion: use a C++ "vector<>" instead of an array...
//    void writeFile(int arraySize, struct bookTable *Book[]) {
//    
//      ofstream outfile;
//      int bookCounter = 0;
//    
//      outfile.open("sale2.txt");
//    
//      outfile << arraySize << endl;
//    
//      for (int i = 0; i < bookCounter; i++) {
//    
//          outfile << Book[i].title << endl;
//          outfile << Book[i].author << endl;
//          outfile << fixed << setprecision(2) << Book[i].price << endl;
//      }
//    
//      outfile.close();
//    
//      delete[] Book;
//    
//    }

int main() {

    // setStruct();  // Not needed
    struct bookTable *book_table = setArray();  // Allocate space
    readFile(book_table);  // Initialize data
    displayMenu(book_table); // use book_table
    // writeFile(); // TBD

    cout << "\nSale2.txt has been created." << endl;

    return 0;
} 

主要说明：

1. 当你在“main（）”中拥有所有内容时，所有代码都可以看到所有变量。

2. 当您将所有内容移动到单独的函数中时，函数将无法再“看到”这些变量。

   这被称为“范围”

3. 一种解决方案是将所有内容放回“main（）”中。 这是不好的。

   另一种解决方案是使您的变量全局化。 这也是坏事。

   一个好的解决方案是在“main（）”中声明需要共享的变量，然后将它们作为参数传递。 这就是我上面所说的。

4. 更好，更高级的解决方案可能是将您的程序重构为类 。

5. 由于您使用C ++进行编程，并且由于您具有可变数量的元素，因此将数组更改为C ++ 向量可能是个好主意。 这有几个优点，包括：

   一个。 您不再需要阅读整个文件只是为了找到＃/ elements - 您可以随意添加新元素。

   湾 您始终可以查询“vector.size（）”以查找当前的＃/元素。

6. 还有其他问题。

我希望有帮助......如果您有任何疑问，请回复。

Answer 2

几件事：
- 您的结构不需要在setStruct函数内部，setStruct应该用于将数据发送到现有结构（下面的示例）
-setArray在被调用时没有被传递任何参数（它需要(int &arraySize, struct bookTable *Book[]) ）并且你的其他函数都不是，这意味着它们实际上没有任何数据需要修改。
应该像这样调用它们： setArray(size of array, struct being passed to it);

另外，应该单独定义setStruct和struct的示例：

struct bookTable {
    string title;
    string author;
    double price;
};
void setStruct(&struct x, string title, string author, double price) {
    x.title  = title;
    x.author = author;
    x.price  = price;

}

确保注意每个函数正在做什么，以便您知道要传递给它们的参数，并更好地理解整体代码。
通过拆分的main（）成一束的功能你是不是真的做太多，除了使你的代码模块化，清晰

另外，发布您正在获得的确切错误将有所帮助，因为我想即使你修复了我提到的这些事情后我也可能无法正常工作

Answer 3

对于初学者：

void setStruct() {

    struct bookTable {
        string title;
        string author;
        double price;
    };
}

您创建一个函数setStruct()然后在其他函数中多次使用它而无需访问函数本身。 为什么不将结构放在其全局范围内，以便在Main()或其他任何地方使用它，并在函数之间自由传递struct声明？

也：

for (int i = 0; getline(infile, Book[i].title); i++) {

    getline(infile, Book[i].author, '\n');
    infile >> Book[i].price;
    infile.ignore(100, '\n');

    bookCounter++;
}

您传递一个use Book ，就好像它在您声明它并可能定义它的范围内一样。 但是，您通过函数传递它 - 意味着结构类型现在超出范围，并且需要通过指针访问其元素。 因此，您的代码需要进行调整：

void readFile(struct bookTable *Book[]) {

    ifstream infile;
    int bookCounter = 0;

    infile.open("books2.txt");

    for (int i = 0; getline(infile, Book[i]->title); i++) {

        getline(infile, Book[i]->author, '\n');
        infile >> Book[i]->price;
        infile.ignore(100, '\n');

        bookCounter++;
    }

    infile.close();
}

请注意，你有Book[i].variable每个地方现在都是Book[i]->variable - 希望这会Book[i].variable帮助。