C++quit(）函数中可能存在作用域问题

尝试声明和初始化选择以具有除"Q"之外的另一个值，并返回该值，以便do-white循环继续运行。我似乎无法从名为quit((的函数内部更改选择变量的值。选择变量是在get_selection((函数中定义的。我对编码和C++还很陌生，有人能帮我吗？我不知道一旦有人输入"q"或"q"退出循环，如何更改select的值以保持do-white循环运行。源代码如下。这是我的第一个堆栈溢出问题。如果我问这个问题的方式不好，请给予建设性的反馈，以便我从中吸取教训，下次做得更好。非常感谢你抽出时间，希望你有一个幸福的一天。

#include <iostream>
#include <vector>
using namespace std;
// Function Prototypes
void display_menu();
char get_selection();
void print_numbers(const vector<int> &list);
void add_number(vector<int> &list);
void remove_number(vector<int> &list);
void display_mean(const vector<int> &list);
void smallest_number(const vector<int> &list);
void largest_number(const vector<int> &list);
char quit();
void handle_unknown();
// End of Function Prototypes
void display_menu() {
cout << "-------------------------------------------n";
cout << "Please select one of the following choices:|n ";
cout << "P - Print Numbers                         |n ";
cout << "A - Add a Number                          |n ";
cout << "R - Remove a Number                       |n";
cout << " M - Display Mean of the Numbers           |n ";
cout << "S - Display the Smallest Number           |n ";
cout << "L - Display the Largest Number            |n ";
cout << "Q - Quit                                  |n ";
cout << "-------------------------------------------n";
cout << "nEnter Selection Here: ";
}
char get_selection() {
char selection {};
cin >> selection;
return toupper(selection);
}
void print_numbers(const vector<int> &list) {
// if the User selects P it will display the list within brackets
cout << "n============================================n"; 
cout << "n[ ";
for ( auto index : list) {
cout<< index << " ";
}
cout << "]";
cout << "nn============================================nn";
}
void add_number(vector<int> &list) {
// if the user selects A it will Add a Number to the list
int number {};
cout << "n==========================================================nn";
cout << "- Please enter a number to be ADDED to the list: ";
cin >> number;
list.push_back(number);
cout << "- The number " << number << " was ADDED to the listnn";
cout << "==========================================================nn";
}
void remove_number(vector<int> &list) {
// if the user selects R it will REMOVE a Number from the list
char choice {};
cout << "n- If you select Yes the last number you added to the list will be REMOVED from the list(Y/N): ";
cin >> choice;
if ( (choice == 'Y' || choice == 'y') && list.size() == 0) {
cout << "- Sorry, but there is currently nothing in the list to remove.nn";
cout << "==========================================================================================================nn";
}
else if (choice == 'Y' || choice == 'y'){
list.pop_back();
cout<< "- The last number you entered was removed from the listnn";
cout << "==========================================================================================================nn";
}
else if (choice == 'N' || choice == 'n') {
cout << "- The number survived the purge!!!nn";
cout << "==========================================================================================================nn";
}
else {
cout << "- You did not enter a valid response, no action was takennn";
cout << "==========================================================================================================nn";
}
}
void display_mean(const vector<int> &list) {
// if the user selects M it will display the mean of the numbers
cout << "n===============================================================nn";
int sum {}; //all the integers in the list added together
double mean {}; // the sum / list.size()
for ( auto integer : list) {
sum = sum + integer;
}
mean = static_cast<double>(sum) / list.size();
cout << "- The Sum of all the numbers in the list is: " << sum << endl;
cout << "- The Mean of all the numbers in the list is: " << mean << endl;
cout << "n===============================================================n";
}
void smallest_number(const vector<int> &list) {
// Displays the smallest number
cout << "n=========================================================nn";
int min = list.at(0);
for ( auto nums : list ) {
if ( nums < min) {
min = nums;
}
} 
cout << "- The Min in the list is: " << min << endl;
cout << "n=========================================================nn";
}

void largest_number(const vector<int> &list) {
// Displays the largest number
cout << "n=========================================================nn";
int max = list.at(0);
for ( auto nums : list ) {
if ( nums > max) {
max = nums;
}
} 
cout << "- The Max in the list is: " << max << endl;
cout << "n=========================================================nn";
}
char quit() {
// Are you sure you want to quit prompt
char quit_prompt {};
cout << "n==============================================nn";
cout << "Are you sure you want to quit (Y/N)? ";
cin >> quit_prompt;
if ( quit_prompt == 'Y' || quit_prompt == 'y') {
cout << "Have a blessed day!!!" << endl;
cout << "n==============================================nn";
return 'a';
}
else if ( quit_prompt == 'N' || quit_prompt == 'n') {
cout << "Choose a optionn";
cout << "n==============================================nn";
display_menu();
return get_selection();
}
else if ( quit_prompt == 'Q' || quit_prompt == 'q') {
cout << "Have a blessed day!!!n";
cout << "n==============================================nn";
return 'a';
}
else {
cout << "You entered a invalid response, no action was takenn";
cout << "n==============================================nn";
display_menu();
return get_selection();
}
}
void handle_unknown() {
cout << "Unknown selection - try again" << endl;
}
int main() {
vector<int> list {1,2,3}; //have to create the list outside of the loop otherwise the loop will 
reset the list every single time the loop resets (lesson learned)
// user input a character that will get saved to this selection variable
char selection {};
// run this loop unless the user inputs 'Q' or 'q'
do {
// tells the user to enter a valid choice if they don't
display_menu();
selection = get_selection();
switch (selection) {
case 'P':
print_numbers(list);
break;
case 'A':
add_number(list);
break;
case 'R':
remove_number(list);
break;
case 'M':
display_mean(list);
break;
case 'L':
largest_number(list);
break;
case 'S':
smallest_number(list);
break;
case 'Q':
quit();
break;
default:
handle_unknown();
}
} while ( selection != 'Q' ); // using the && logical statement because of the != comparison.
return 0; 
}