为什么即使我放了一个 break 语句，我的程序也会一直循环

Question

我正在尝试制作日志程序，但遇到了这个问题。即使有 break 语句，它也总是循环。

这是我在 while 循环中使用 break 语句的部分，但它一直在无休止地循环。

void userPrompt(){
            while(true){
                cout << "[1] Log in\n";
                cout << "[2] Log out\n";
                cout << "[3] View Log Book\n";
                cout << "[0] Exit\n";
                cout << "Choice: ";
                cin >> choice;
                cout << endl;
                switch(choice){
                    case 1:
                        logIn();
                        break;
                    case 2:
                        logOut();
                        break;
                    case 3:
                    viewRecords();
                        break;
                    case 4:
                        break;
                    default:
                        cout<<"Invalid Choice. PLease try again\n";
                        break;
                }
            }
        }

这是完整的代码

#include<string>
using namespace std;
struct node{
    string name;
    int timeIn, timeOut;
    node* nextNode;
};
class LogBook{
    private:
        node* head = NULL;
        node* tail = NULL;
        int choice;
    public:
        void userPrompt(){
            while(true){
                cout << "[1] Log in\n";
                cout << "[2] Log out\n";
                cout << "[3] View Log Book\n";
                cout << "[0] Exit\n";
                cout << "Choice: ";
                cin >> choice;
                cout << endl;
                switch(choice){
                    case 1:
                        logIn();
                        break;
                    case 2:
                        logOut();
                        break;
                    case 3:
                    viewRecords();
                        break;
                    case 4:
                        break;
                    default:
                        cout<<"Invalid Choice. PLease try again\n";
                        break;
                }
            }
        }
        void logIn(){
            string name;
            int time;
            node* temp = new node();
            cout << "Enter your name: ";
            cin >> name;
            cout << "Time in: ";
            cin >> time;
            cout << endl;
            temp->name = name;
            temp->timeIn = time;
            temp->nextNode = NULL;
            
            if(head == NULL){
                head = temp;
                tail = temp;
            }
            else{
                tail->nextNode = temp;
                tail = tail->nextNode;
            }
        }
        void logOut(){
            string name;
            int time;
            node* temp;
            temp = head;
            cout << "Enter Name: ";
            cin >> name;
            while(temp != NULL){
                if(temp->name == name){
                    cout << "Time out: ";
                    cin >> time;
                    temp->timeOut = time;
                }
                else
                cout << "Name not found\n";
                    break;
            }
        } 
        void viewRecords(){
            node* temp;
            temp = head;
            while(temp != NULL){
                cout << "\nLog records:\n";
                cout << "Name: " << temp->name << endl;
                cout << "Time in: " << temp->timeIn << endl;
                cout << "Time out: " << temp->timeOut << endl;
                temp = temp->nextNode;
            }
        }
};
int main(){
    LogBook user1;
    user1.userPrompt();
    return 0;
}`

Answer 1

所有的 break 语句都在 switch 中。所以他们正在突破switch 并回到while 循环（然后无限循环）。

除非您放置break，否则switch 语句将传递给其他case 语句，因此那些break 调用只是终止该特定情况。

您需要在while 的顶层某处使用break 语句来表示您想要停止，因为您的条件是while(true)。否则它将永远循环。

Answer 2

你使用的break语句只是break switch语句，你还需要为while循环添加break语句