C++ 试图声明函数的局部变量，但获取作用域错误

下面是我的一小段代码。您在这里看到的代码片段有两个目的：1）显示一个菜单——这是menu（）函数；2）提示用户进行选择并存储它——selection（）

selection（）从第18行开始

我试图声明一些变量，这些变量将是我的menu（）和selection（）函数的局部变量，但我会遇到如下错误，对于我试图声明的所有内容：

警告：未使用的变量's'（它为我的所有'char'变量提供了此选项） 或 错误：“snack_selection”未在此范围内声明（它为我试图声明的两个“int”变量提供了此选项）

但这怎么可能呢？我不知道我错过了什么

感谢患者的反馈

int menu(void)
{  
    cout << "Available snacks to select from: " << endl  //presents menu
         << "     " << setw(5) << "P - Potato Chips" << setw(9) << "$1.25" 
         << endl  //prompts user to make a selection (until it is valid)
         << "     " << setw(5) << "S - Snickers Bar" << setw(9) << "$1.35" 
         << endl
         << "     " << setw(5) << "T - Pop Tart" << setw(13) << "$0.95"
         << endl
         << "     " << setw(5) << "C - Cookies" << setw(14) << "$1.50"
         << endl
         << "     " << setw(5) << "B - Brownie" << setw(14) << "$1.75"
         << endl
         << "     " << setw(5) << "N - Nuts" << setw(17) << "$1.40"
         << endl;
    selection();
    return 0;
}

int selection(void)   //FUNCTION: welcomes, presents menu, and prompts user for selection
{

    int potato_chip_price = 125, snickers_bar_price = 135, pop_tart_price = 95, cookies_price = 150, brownie_price = 175, nuts_price = 140;
    char snack_selection = 0; //condition for snack_selection switch case statement
    char P, S, T, C, B, N;  //the char variables needed for the snack_selection 


    cout << "Please enter the letter labeling your snack selection: ";
    cin >> snack_selection;
    cout << endl;

    switch(std::toupper(snack_selection))  
    { //beginning of switch statement (goes through all the "legal" options so there is an "illegal" option
    case 'P': price = potato_chip_price; //setting it up this way stores the value of price with the value of potato_chip_price. if the other way around, pop_tart_price would become 0 since that is what price is set to.
        break;
    case 'S': price = snickers_bar_price; //stores the snack selection price in CENTS to the int price variable needed for the next function's argument
        break;
    case 'T': price = pop_tart_price;
        break;
    case 'C': price = cookies_price;
        break;
    case 'B': price = brownie_price;
        break;
    case 'N': price = nuts_price;
        break;
    default:
        cout << "Invalid selection!";
        menu();
    } //end of switch statement
    return(price); //needs to return some kind of value bc it isn't a void function, and compiler will give a warning
}

int菜单（无效）
{  
cout代码编译得很好，但包含未使用变量的警告。在3个位置声明未使用的
char
变量。删除这些声明可以消除警告。这里我发布了修改后的代码

#include <iostream>
#include <iomanip>
#include <cctype>
using namespace std;

//Variable Declarations

int price = 0, total_paid = 0, total_price = 0; //arguments for the three functions in the program.need to be global

//Function Declarations: 

int menu(void);
// presents menu

int selection(void);
//prompts user to make selection and stores it

int accept_money(int price);
//tells user what money it accepts and the label for each type
//1. repeats back what cost is
//2. tells what  has been paid
//3. allows user to input money by payment selection here

int compute_change(int total_paid, int total_price);
//1.  tells user what total amt was paid
//2.  computes change
//3.  tells user what change will be
//4.  ask user if he or she would like another purchase (if statement. if y, send back to int menu(). if no, thank for purchase message.)

int main()
{
    cout << "Welcome to the snack vending machine" << endl << endl;

    menu();
    accept_money(price);
    compute_change(total_paid, total_price);

    return 0;
}

//Function Definitions

int menu(void)
{
    cout << "Available snacks to select from: " << endl  //presents menu
        << "     " << setw(5) << "P - Potato Chips" << setw(9) << "$1.25"
        << endl  //prompts user to make a selection (until it is valid)
        << "     " << setw(5) << "S - Snickers Bar" << setw(9) << "$1.35"
        << endl
        << "     " << setw(5) << "T - Pop Tart" << setw(13) << "$0.95" <<
        endl
        << "     " << setw(5) << "C - Cookies" << setw(14) << "$1.50" <<
        endl
        << "     " << setw(5) << "B - Brownie" << setw(14) << "$1.75" <<
        endl
        << "     " << setw(5) << "N - Nuts" << setw(17) << "$1.40" <<
        endl;
    selection();
    return 0;
}

int selection(void)   //FUNCTION: welcomes, presents menu, and prompts user for selection
{
    int potato_chip_price = 125, snickers_bar_price = 135, pop_tart_price = 95, cookies_price = 150, brownie_price = 175, nuts_price = 140;
    char snack_selection = 0; //condition for snack_selection switch case statement

    cout << "Please enter the letter labeling your snack selection: ";
    cin >> snack_selection;
    cout << endl;

    switch ( std::toupper(snack_selection) )
    { //beginning of switch statement (goes through all the "legal" options so there is an "illegal" option
    case 'P': price = potato_chip_price; //setting it up this way stores the value of price with the value of potato_chip_price. if the other way around, pop_tart_price would become 0 since that is what price is set to.
        break;
    case 'S': price = snickers_bar_price; //stores the snack selection price in CENTS to the int price variable needed for the next function's argument
        break;
    case 'T': price = pop_tart_price;
        break;
    case 'C': price = cookies_price;
        break;
    case 'B': price = brownie_price;
        break;
    case 'N': price = nuts_price;
        break;
    default:
        cout << "Invalid selection!";
        menu();
    } //end of switch statement
    return(price); //needs to return some kind of value bc it isn't a void function, and compiler will give a warning
}


int accept_money(int price)
{
    int nickel = 5, quarter = 25, dollar = 100;
    char money_selection = 0; //condition for money_selection switch case statement

    cout << "Money accepted by the machine:\n"
        << "     " << setw(5) << "N - Nickel" << endl
        << "     " << setw(5) << "Q - Quarter" << endl
        << "     " << setw(5) << "D - Dollar" << endl << endl;

    do
    {
        cout << "Your selected snack item cost: " << price << " CENTS" << endl
            << "Your total inserted: " << total_paid << " CENTS" << endl
            << "Insert amount (enter letter of choice): ";
        cin >> money_selection;
        cout << endl;
        switch ( std::tolower(money_selection) )
        {
        case 'n': total_paid = nickel + total_paid;
            cout << endl;
            break;
        case 'q': total_paid = quarter + total_paid;
            cout << endl;
            break;
        case 'd': total_paid = dollar + total_paid;
            cout << endl;
            break;
        default:
            cout << money_selection << " is not recognized as a coin." << endl << endl;
        }
    } while ( total_paid < price );
    return total_paid;  //this function needs to return updated value, or any changes made to it will remain local to the function
}

int compute_change(int total_paid, int total_price)
{
    char continue_purchase = 0;

    int change = total_paid - price; //has to have somewhere to be stored in this function to work
    int amt_inserted = total_paid; //was not using updated value of total_paid from previous fnction, so had to save it to a variable local to this one from the global variable

    cout << "Your total inserted: " << amt_inserted << " CENTS" << endl
        << "Dispensing change: " << change << setw(5) << " CENTS" << endl
        << "Would you care to make another purchase (Y/N): ";
    cin >> continue_purchase;

    switch ( std::tolower(continue_purchase) )
    {
    case 'y': total_paid = 0;
        price = 0;
        total_price = 0;
        cout << endl << endl;
        menu();
        break;
    case 'n': cout << "Thank you and enjoy your purchase!";
        break;
    default:
        cout << "Invalid Selection" << endl << endl;
        compute_change(total_paid, total_price);
    }
    return 0;
}

#包括
#包括
#包括
使用名称空间std；
//变量声明
int price=0，total_paid=0，total_price=0；//程序中三个函数的参数。必须是全局参数
//函数声明：
int菜单（无效）；
//赠送菜单
int选择（void）；
//提示用户进行选择并将其存储
国际货币（国际价格）；
//告诉用户它接受多少钱以及每种类型的标签
//1.重复成本是多少
//2.说明已支付的金额
//3.允许用户在此处通过付款选择输入资金
int计算变更（支付的int总额，支付的int总价）；
//1.告诉用户支付的总金额
//2.计算更改
//3.告诉用户将进行哪些更改
//4.询问用户是否希望再次购买（如果是语句，则返回int menu（）。如果不是，则感谢购买消息。）
int main（）
{
cout除了大家在评论中提到的不使用全局变量和其他良好编程实践之外，代码本身编译得很好（除非您在编译器标志中像我一样激活了-Werror开关），但有警告

您似乎误解了，如果要在case语句中使用字符串文字“p”，就像在函数
int selection（void）中所做的那样
，您必须首先声明一个变量
char P
。使用这些字符串文字不必声明变量。变量char P和字符串“P”之间没有任何联系

警告来自以下几行：

在函数
int compute\u change（int total\u paid，int total\u price）
中删除以下行：

char y;

char n, q, d; //the char variables needed for the money_selection switch case statement

然后在函数
int accept\u money（int price）
中删除以下行：

char y;

char n, q, d; //the char variables needed for the money_selection switch case statement

最后在函数
int selection（void）//函数中：欢迎、显示菜单并提示用户选择

拆下以下行

char P, S, T, C, B, N;  //the char variables needed for the snack_selection switch case statement (can't be inside function, needs to be global

在那之后你会没事的

如果你真的想使用这些变量，p，S等等，那么你应该给它们赋值并声明它们为常量。我在这里做了一个例子，让你看看。你可以按照类似的思路做其余的事情

int compute_change(int total_paid, int total_price)
{
    char continue_purchase = 0;
    const char y = 'y';

    int change = total_paid - price; //has to have somewhere to be stored in this function to work
    int amt_inserted = total_paid; //was not using updated value of total_paid from previous fnction, so had to save it to a variable local to this one from the global variable

    cout << "Your total inserted: " << amt_inserted << " CENTS" << endl
         << "Dispensing change: " << change << setw(5) << " CENTS" <<
            endl
         << "Would you care to make another purchase (Y/N): ";
    cin >> continue_purchase;

    switch(std::tolower(continue_purchase))
    {
    case y:
        total_paid = 0;
        price = 0;
        total_price = 0;
        cout << endl << endl;
        menu();
        break;
    case 'n': cout << "Thank you and enjoy your purchase!";
        break;
    default:
        cout << "Invalid Selection" << endl << endl;
        compute_change(total_paid, total_price);
    }
    return 0;
}

编译器会警告您未使用的变量/参数，因为它会显示您的疏忽/遗漏等真正错误（例如，在本例中，您似乎误解了声明char变量需要使用与该char变量名称包含相同文本的字符串文字）。有关此问题的详细信息，请参阅此问题：

希望对您有所帮助。
您显示的代码从未声明名为
d
、未使用或其他的变量。您引用的错误消息似乎与未显示的某些代码有关。您从未声明
price
？在
菜单（）
之前添加
选择（）的原型或移动
选择（）的定义
在
菜单（）之前
字符P、S、T、C、B、N；
这些变量都没有被使用。这些是名为
P
、
S
等的
char
类型的变量，与literal
char
值
'P'
、
'S'
等明显不同。删除这一行将消除一些关于未使用变量的警告。您需要发布错误消息的完整来源（包括任何
#include
指令）和完整文本，与屏幕上显示的内容完全一致。使用链接可为您的问题添加必要的信息。