Visual Studio 2017中C++ do-while循环异常重复且不等待输入求助

我帮你拆解下代码里的问题，这些正是导致循环异常、输入不停止的根源：

核心问题点 #

1. do-while循环条件是赋值而非判断 #

你的循环条件写的是：

} while (answer = 1);

这里answer = 1是赋值操作，会把1强制赋给answer，并且这个表达式的结果永远是true，所以循环会无限执行，不管你输入什么都会一直重复。正确的写法应该是相等判断：

} while (answer == 1);

2. 输入类型不匹配导致输入流失效 #

answer被定义为int类型，但你让用户输入的是字符Y/N。当用户输入字符（比如'n'）时，cin无法将字符转换为整数，会触发输入流的失败状态（failbit）。一旦输入流失效，后续所有的cin操作都会直接跳过，不会等待用户输入，这就是你看到“本该等待输入的位置不停止”的原因。

3. switch语句缺少break，逻辑完全混乱 #

第二个switch里的case没有加break，导致匹配任意case后都会执行后续所有代码：

switch (answer) {
case 1: answer = 1;
case 'n': answer = 1;
default: answer = 2;
}

比如输入1时，会先执行answer=1，然后因为没有break，继续走到default把answer改成2；输入'n'时，因为answer是int，'n'的ASCII值是110，所以会直接走到default设置answer=2，完全不符合你的预期。

4. 月份数组初始化错误 #

你的month数组中，"August"和"September"之间少了一个逗号，导致这两个字符串被拼接成一个，数组长度变成11而不是12，后续访问month[8]及以后会出现越界问题：

// 错误写法
string month[] = { "January", "February", "March", "April", "May", "June", "July", "August"
"September", "October", "November", "December" };
// 正确写法
string month[] = { "January", "February", "March", "April", "May", "June", "July", "August",
"September", "October", "November", "December" };

5. 第一个switch仅处理了1月，其他月份无逻辑 #

当前代码只有case 1处理了1月的日期判断，输入其他月份数字时，switch里什么都不做，建议补充其他月份的逻辑，或者添加default提示输入无效。

修复后的完整代码 #

#include "stdafx.h"
#include<iostream>
#include<string>
#include<limits> // 用于处理输入流清空
using namespace std;

int main() {
    // 修复数组逗号问题
    string month[] = { "January", "February", "March", "April", "May", "June", 
                       "July", "August", "September", "October", "November", "December" };
    int m, d;
    // 把answer改成char类型，匹配用户输入的Y/N
    char answer;

    cout << "Welcome 2018!!!" << endl;
    do {
        cout << "Enter the number corresponding to the month you want displayed" << endl;
        // 处理输入错误：如果输入不是整数或超出1-12范围，重新输入
        while (!(cin >> m) || m < 1 || m > 12) {
            cin.clear(); // 重置输入流状态
            cin.ignore(numeric_limits<streamsize>::max(), '\n'); // 清空缓冲区的错误输入
            cout << "Invalid input! Please enter a number between 1 and 12: ";
        }

        switch (m) {
        case 1:
            cout << month[0] << endl;
            cout << "Enter the date to know the day it is/will be" << endl;
            // 处理日期输入错误
            while (!(cin >> d) || d < 1 || d > 31) {
                cin.clear();
                cin.ignore(numeric_limits<streamsize>::max(), '\n');
                cout << "Invalid date! Please enter a number between 1 and 31: ";
            }
            if (d == 7 || d == 14 || d == 21 || d == 28) {
                cout << "The day on " << d << " January is Sunday!" << endl;
            }
            else if (d == 1 || d == 8 || d == 15 || d == 22 || d == 29) {
                cout << "The day on " << d << " January is Monday!" << endl;
            }
            else if (d == 2 || d == 9 || d == 16 || d == 23 || d == 30) {
                cout << "The day on " << d << " January is Tuesday!" << endl;
            }
            else if (d == 3 || d == 10 || d == 17 || d == 24 || d == 31) {
                cout << "The day on " << d << " January is Wednesday!" << endl;
            }
            else if (d == 4 || d == 11 || d == 18 || d == 25) {
                cout << "The day on " << d << " January is Thursday!" << endl;
            }
            else if (d == 5 || d == 12 || d == 19 || d == 26) {
                cout << "The day on " << d << " January is Friday!" << endl;
            }
            else if (d == 6 || d == 13 || d == 20 || d == 27) {
                cout << "The day on " << d << " January is Saturday!" << endl;
            }
            break; // 添加break，避免后续case串流
        // 可以在这里补充其他月份的case逻辑
        default:
            cout << month[m-1] << endl;
            cout << "Day lookup logic for this month is not implemented yet." << endl;
            break;
        }

        cout << "Are you sure you want to quit?" << endl;
        cout << "Enter Y/N based on your choice: ";
        // 清空缓冲区残留的换行符，避免直接读取空字符
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
        cin >> answer;

        // 统一转换为小写，兼容大小写输入
        answer = tolower(answer);
        // 调整逻辑：输入'n'继续循环，输入'y'退出
        switch (answer) {
        case 'n':
            answer = 1;
            break;
        case 'y':
            answer = 2;
            break;
        default:
            cout << "Invalid input! Assuming you want to continue." << endl;
            answer = 1;
            break;
        }
    } while (answer == 1); // 修复为相等判断

    cout << "Thank You and Come Again!!!" << endl;
    return 0;
}

额外优化说明 #

• 把answer改成char类型，完美匹配用户输入的字符；
• 添加了输入错误处理：当用户输入非整数或超出范围的数字时，会提示并重新等待输入；
• 对输入的字符统一转小写，不管用户输入'N'还是'n'都能正确识别；
• 补充了第一个switch的default分支，处理其他月份的情况；
• 所有case都添加了break，彻底避免逻辑串流。

现在运行修复后的代码，应该就能正常等待输入，循环也会按照你的预期执行了！

内容的提问来源于stack exchange，提问作者Anonymous