错误：classname没有命名类型

Question

我是一名从指针开始的中级学生。 我正在尝试将数据存储在一个数组中，稍后由搜索功能调用。 当我尝试编译时，我被告知“错误：零售没有命名类型”，我不明白这意味着什么或如何解决它。

// ********************************************************
// Starting Out with C++                                  *
// From Control Stuctures through Objects                 *
// seventh edition                                        *
//                                                        *
// Chapter 8 Searching and Sorting Arrays                 *
//                                                        *
// Serendipity Booksellers Software Development           *
// Project — Part 8: A Problem-Solving Exercise           *
//                                                        *
// Multi-File Program                                     *
// ********************************************************
#include "bookinfo.h"
#include "cashier.h"
#include "invmenu.h"
#include "reports.h"
#include <iostream>
using namespace std;

// Constant for array sizes
const int SIZE = 20;
// Global Arrays
string bookTitle[SIZE];
string isbn[SIZE];
string author[SIZE];
string publisher[SIZE];
string dateAdded[SIZE];
int qtyOnHand[SIZE];
double wholesale[SIZE];
double retail[SIZE];

retail[SIZE] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19};

wholesale[SIZE] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19};

qtyOnHand[SIZE] = {10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10};


dateAdded[0] = "1/1";
dateAdded[1] = "1/1";
dateAdded[2] = "2/1";
dateAdded[3] = "3/1";
dateAdded[4] = "4/1";
dateAdded[5] = "5/1";
dateAdded[6] = "6/1";
dateAdded[7] = "7/1";
dateAdded[8] = "8/1";
dateAdded[9] = "9/1";
dateAdded[10] = "10/1";
dateAdded[11] = "11/1";
dateAdded[12] = "12/1";
dateAdded[13] = "13/1";
dateAdded[14] = "14/1";
dateAdded[15] = "15/1";
dateAdded[16] = "16/1";
dateAdded[17] = "17/1";
dateAdded[18] = "18/1";
dateAdded[19] = "19/1";


author[0] = "0";
author[1] = "1";
author[2] = "2";
author[3] = "3";
author[4] = "4";
author[5] = "5";
author[6] = "6";
author[7] = "7";
author[8] = "8";
author[9] = "9";
author[10] = "10";
author[11] = "11";
author[12] = "12";
author[13] = "13";
author[14] = "14";
author[15] = "15";
author[16] = "16";
author[17] = "17";
author[18] = "18";
author[19] = "19";

bookTitle[0] = "0";
bookTitle[1] = "1";
bookTitle[2] = "2";
bookTitle[3] = "3";
bookTitle[4] = "4";
bookTitle[5] = "5";
bookTitle[6] = "6";
bookTitle[7] = "7";
bookTitle[8] = "8";
bookTitle[9] = "9";
bookTitle[10] = "10";
bookTitle[11] = "11";
bookTitle[12] = "12";
bookTitle[13] = "13";
bookTitle[14] = "14";
bookTitle[15] = "15";
bookTitle[16] = "16";
bookTitle[17] = "17";
bookTitle[18] = "18";
bookTitle[19] = "19";

isbn[0] = "0";
isbn[1] = "1";
isbn[2] = "2";
isbn[3] = "3";
isbn[4] = "4";
isbn[5] = "5";
isbn[6] = "6";
isbn[7] = "7";
isbn[8] = "8";
isbn[9] = "9";
isbn[10] = "10";
isbn[11] = "11";
isbn[12] = "12";
isbn[13] = "13";
isbn[14] = "14";
isbn[15] = "15";
isbn[16] = "16";
isbn[17] = "17";
isbn[18] = "18";
isbn[19] = "19";


int main()
{
    int choice = 0; // To hold the user's menu choice

    // Display the menu until the user selects item 4
    while (choice != 4)
    {
        cout << "Serendipity Booksellers\n";
        cout << "\tMain Menu\n\n";

        cout << "1.Cashier Module\n";
        cout << "2.Inventory Database Module\n";
        cout << "3.Report Module\n";
        cout << "4.Exit\n\n";

        // Get the menu choice as input from the user
        cout << "Enter Your Choice: ";
        cin >> choice;

        // Validate the user's input
        while (choice < 1 || choice > 4)
        {
            cout << "\nPlease enter a number in the range 1 - 4.\n";

            cout << "Enter Your Choice: ";
            cin >> choice;
        }

        // Display a selection message
        {
            switch (choice)
            {
                case 1:
                    cashier();
                    break;
                case 2:
                    invMenu();
                    break;
                case 3:
                    reports();
                    break;
                case 4:
                    cout << "\nYou selected item 4.\n";
                    break;
            }
        }

        cout << endl << endl;
    }
    return 0;
}

我怎么没能初始化数组？ 我是否错误地格式化了我的声明？

Answer 1

您无法使用以下内容初始化数组：

retail[SIZE] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19};

您可以在声明它时初始化它。

double retail[SIZE] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19};

或者您可以使用for循环设置值。

for (int i = 0; i < 20; ++i )
{
   retail[i] = i;
}

Answer 2

使用C ++ 11初始化列表是一个祝福，并与std :: vector非常匹配：

初始化 ：
std::vector<double> retail {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19};
分配 ：
std::vector<double> retail2; retail2 = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19};

尽量避免C数组，vector有：
- 检查
- 自动内存管理（RAII，自动增长等）
- 迭代器
- 与STL的算法和适配器很好地融合

Answer 3

虽然你最初提出的问题已经解决了，但我认为更大的问题是使用“并行数组” - 这种数据结构是许多错误的根源。 例如，创建用于描述每个书籍条目的结构或类以及维护这些项目的集合要好得多

class BookEntry {

public:
    BookEntry(const std::string &title, const std::string &author, const std::string &isbn, double wholesalePrice, double retailPrice, const std::string &dateAdded, int quantityOnHand = 0)
        : title_m(title), author_m(author), isbn_m(isbn), wholesalePrice_m(wholesalePrice), retailPrice_m(retailPrice), dateAdded_m(dateAdded), quantityOnHand_m(quantityOnHand)
    {

    }

    std::string title_m;
    std::string author_m;
    std::string isbn_m;

    double retailPrice_m;
    double wholesalePrice_m;
    std::string dateAdded_m;

    int quantityOnHand_m;
};

// main.cpp

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

int main(int argc, const char * argv[])
{
    BookEntry bookEntries[] = {
            // Title,                        Author,           ISBN,             Wholesale,      Retail,      DateAdded,       QuantityOnHand
            { "The Hobbit",                  "J.R.R. Tolkein", "978-0547928227", 5.43,           9.77,        "1937-Sep-21",   1234 },
            { "The Fellowship of the Ring",  "J.R.R. Tolkein", "978-0547928210", 7.99,           10.67,       "1954-Jul-29",   4321 },
            { "The Two Towers",              "J.R.R. Tolkein", "978-0547928203", 8.01,           10.68,       "1954-Nov-11",   3214 },
            { "The Return of the King",      "J.R.R. Tolkein", "978-0547928197", 8.43,           10.77,       "1955-Oct-20",   2143 },
            { "The Talisman",                "Stephen King",   "978-1451697216", 4.31,            8.98,       "1984-Nov-08",   3333 }
    };


    for (auto &b : bookEntries) {
        std::cout << "Title: " << b.author_m << "; Author: " << b.author_m << std::endl;
    }

    return 0;
}

请注意，现在如何以一致的方式组织用于初始化BookEntry的数据，以便更容易识别数组中的“记录”，并且更难以将元素输出，从而使整个结构不一致。

在实际操作中，您可能会重构BookEntry以将书籍标识与其库存和定价信息分开，所有这些都将保存在数据库中并从那里初始化，但您仍然希望程序中有一个好的数据模型，不只是大量的并行阵列。

Answer 4

您不能像这样初始化零售，试试这个：

double retail[SIZE] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19};

虽然在使用c++我会建议尝试使用诸如向量之类的stl类型。