如何让C++程序在输入日期无效时停止执行后续运算判断语句

你的代码将「日期合法性校验」和「日期信息、闰年结果输出」设为了完全独立的两段逻辑，无论日期是否合法，后续的输出逻辑都会强制执行，才会出现无效日期同时输出报错和闰年判断的问题。

1. 新增一个布尔类型的合法性标记，初始值为true，用于记录日期是否通过校验
2. 所有触发错误提示的分支中，将标记值改为false
3. 将「打印月份全称」「判断闰年输出」的两段代码，全部包裹在合法性标记为true的判断分支中，只有日期合法时才执行
4. 顺便修正原有代码的两处逻辑bug：
   • 原2月29日合法性判断中的year%400 == 400为错误逻辑，应修改为「不是闰年」的判断条件
   • 原闰年判断中year%400==0的分支为空，没有输出对应闰年提示

#include <iostream>
using namespace std;

int main() {
    int month, day, year;
    cout<<"Enter numeric values for the current date [mm dd yyyy] ->";
    cin>>month>>day>>year;
    // 新增合法性标记
    bool is_date_valid = true;

    if (month > 12 || month < 1){
        cout<<"The month must be in the interval [1,12]. "<<endl;
        is_date_valid = false;
    }
    else if (day > 31 || day < 1){
        cout<<"The day must be in interval [1,31]. "<<endl;
        is_date_valid = false;
    }
    else if (year < 1582){
        cout<<"The year must come after 1582. "<<endl;
        is_date_valid = false;
    }
    else if (month == 2 && day > 29){
        cout<<"The day in February cannot be greater than 29. "<<endl;
        is_date_valid = false;
    }
    // 修正此处闰年判断逻辑
    else if (month == 2 && day == 29 && !(year%400==0 || (year%4 == 0 && year%100 !=0))){
        cout<<"February cannot have 29 days in a common year. "<<endl;
        is_date_valid = false;
    }
    else if (month == 4 && day == 31){
        cout<<"The day in April cannot be 31. "<<endl;
        is_date_valid = false;
    }
    else if (month == 6 && day == 31){
        cout<<"The day in June cannot be 31. "<<endl;
        is_date_valid = false;
    }
    else if (month == 9 && day == 31){
        cout<<"The day in September cannot be 31. "<<endl;
        is_date_valid = false;
    }
    else if (month == 11 && day == 31){
        cout<<"The day in November cannot be 31. "<<endl;
        is_date_valid = false;
    }

    // 只有合法日期才执行后续输出
    if (is_date_valid) {
        if (month==1){
            cout<<"The date January "<<day<<", "<<year;
        }
        else if (month==2){
            cout<<"The date February "<<day<<", "<<year;
        }
        else if (month==3){
            cout<<"The date March "<<day<<", "<<year;
        }
        else if (month==4){
            cout<<"The date April "<<day<<", "<<year;
        }
        else if (month==5){
            cout<<"The date May "<<day<<", "<<year;
        }
        else if (month==6){
            cout<<"The date June "<<day<<", "<<year;
        }
        else if (month==7){
            cout<<"The date July "<<day<<", "<<year;
        }
        else if (month ==8){
            cout<<"The date August "<<day<<", "<<year;
        }
        else if (month == 9){
            cout<<"The date September "<<day<<", "<<year;
        }
        else if (month==10){
            cout<<"The date October "<<day<<", "<<year;
        }
        else if (month == 11){
            cout<<"The date November "<<day<<", "<<year;
        }
        else if (month == 12) {
            cout<<"The date December "<<day<<", "<<year;
        }

        // 修正此处闰年判断的空分支问题
        if (year%400==0 || (year%4 == 0 && year%100 !=0)){
            cout<<" is in a leap year."<<endl;
        }
        else {
            cout<<" is in a common year."<< endl;
        }
    }

    return 0;
}

内容的提问来源于stack exchange，提问作者Paul