C++類變量範圍

Question

我對C++類中的變量作用域有個疑問。我正在處理的問題是創建一個包含結構數組的類，每個結構都保存特定類型飲料的名稱，成本和金額。

該類應該有公共成員函數來購買飲料並顯示菜單，以及用於獲取和驗證貨幣輸入（由buy_drink調用）的私有函數，並顯示日期結束報告（由析構函數調用）。

我在私有函數input_money中的範圍有問題。我得到一個錯誤，說該數組尚未定義。我測試了display_data函數（用於打印菜單），並且它自己運行良好，但是現在我無法弄清楚爲什麼input_money會產生範圍錯誤，而display_data不會。這裏是頭文件：

/* need to create a class that holds an array of 
    5 structures, each structure holding string drink name, 
    double cost, and int number in machine 

    class needs public functions to display data and 
    buy drink 

    private functions input money -- called by buy_drink to accept, 
    validate, and return to buy drink the amount of money input 

    daily report -- destructor that reports how much money 
    was made daily and how many pops are left in machine */ 

#ifndef DRINKS_H 
#define DRINKS_H 
#include <string> 

class Drinks 
{ 
private: 
    struct Menu 
    {         
    std::string name;     
    double cost; 
    int number; 
    }; 
    Menu list[5];    // array of 5 menu structures 
    double money_made;  // track money made during the day 
    double input_money(int); // return validated money to buy_drink() 
    void daily_report();  // called by deconstructor 

public: 
    Drinks();    
    ~Drinks();    
    void display_data(); 
    void buy_drink(int); 
}; 
#endif 

這裏是實現文件：

/* implementation file for Drinks class */ 

#include <iostream> 
#include <string> 
#include "drinks.h" 
using namespace std; 

const int SIZE = 5; 
const int START_SIZE = 100; 

Drinks::Drinks() 
{ 
    list[0].name = "Coke"; 
    list[1].name = "Root Beer"; 
    list[2].name = "Orange Soda"; 
    list[3].name = "Grape Soda"; 
    list[4].name = "Bottled Water"; 

    for (int count = 0; count < (SIZE-1); count++) 
    list[count].cost = .75; 
    list[4].cost = 1; 

    for (int count = 0; count < SIZE; count++) 
    list[count].number = 20; 

    money_made = 0; 
} 

void Drinks::display_data() 
{ 
    for (int count = 0; count < SIZE; count++) { 
    if (count == 0) 
     cout << count+1 << list[count].name << "\t\t$ "; 
    else 
     cout << count+1 << list[count].name << "\t$ "; 
    cout << list[count].cost << "\t" 
    << list[count].number << endl; 
    } 
} 

double input_money(int c) 
{ 
    double input; 

    cin >> input; 

    while (input != list[c].cost) { 
    if (input < list[c].cost) { 
     cout << "Not enough money.\n" 
     << "Enter " << list[c].cost - input 
     << " more cents to buy\n\n> "; 
     cin >> input; 
    } 
    else if (input > list[c].cost) { 
     cout << "Too much money.\n" 
     << "I only need $" << list[c].cost << endl 
     << "Enter " << input - list[c].cost 
     << " less money: "; 
     cin >> input; 
    } 
    } 

    return input; 
} 

void Drinks::buy_drink(int c)    // this receives an int choice (to access corresponding structure in the list array) 
{ 
    double input;        
    cout << "Enter " <<list[c].cost    
     << " to purchase " << list[c].name  
     << "\n\n> ";       
    input = input_money(c);     // input money returns a validated and accurate price for the drink and is passed the choice to access array 

    list[c].number -= 1; 
    money_made += list[c].cost;    // add cost of drink to money made 
} 

void Drinks::daily_report() 
{ 
    int end_size = 0; 

    for (int count = 0; count < SIZE; count++) 
    end_size += list[count].number; 

    cout << "Today, you made $" << money_made << endl; 
    cout << "There are " << START_SIZE - end_size 
     << " drinks left in the machine" << endl; 
} 

Drinks::~Drinks() 
{ 
    daily_report(); 

    cout << "goodbye mr anderson\n"; 
} 

任何幫助，將不勝感激！我似乎無法弄清楚爲什麼input_money函數不能訪問數組中的結構。

謝謝！

編輯：總noob錯誤/粗心。忘記在input_money函數定義中添加類的名稱並使用範圍解析運算符（即應該是Drinks :: input_money（int c））。感謝那些回答。

Answer 1

double Drinks::input_money(int c) 
    // ^^^^^^^^ forgot this 

您在提供實現時忘記了類名。

Answer 2

通知

void Drinks::display_data

和

double input_money(int c)

您的定義之間的差別在第二種情況下，你已經定義了一個免費的功能，是不是類的成員，具有沒有關於班級成員的信息。它應該是

double Drinks::input_money(int c)