#include <iostream>
using namespace std;
class Date
{
    int day;
    int month;
    int year;
public:
    Date() : day(0), month(0), year(0) {}
    void input()
    {
        cout << "Enter day: ";
        cin >> day;
        cout << "Enter month: ";
        cin >> month;
        cout << "Enter year: ";
        cin >> year;
    }
    bool isValid()
    {
        if (month < 1 || month > 12)
            return 0;
        if (day < 1 || day > 31)
            return 0;
        if ((month == 4 || month == 6 || month == 9 || month == 11) && day > 30)
            return 0;
        if (month == 2)
        {
            if (year % 4 == 0)
            {
                if (day > 29)
                    return 0;
            }
            else
            {
                if (day > 28)
                    return 0;
            }
        }

        return 1;
    }
};
int main()
{
    Date date;
    date.input();
    if (date.isValid())
        cout << "Valid date." << endl;
    else
        cout << "Invalid date." << endl;
    return 0;
}#include <iostream>
using namespace std;
class Date
{
    int day;
    int month;
    int year;
public:
    Date() : day(0), month(0), year(0) {}
    void input()
    {
        cout << "Enter day: ";
        cin >> day;
        cout << "Enter month: ";
        cin >> month;
        cout << "Enter year: ";
        cin >> year;
    }
    bool isValid()
    {
        if (month < 1 || month > 12)
            return 0;
        if (day < 1 || day > 31)
            return 0;
        if ((month == 4 || month == 6 || month == 9 || month == 11) && day > 30)
            return 0;
        if (month == 2)
        {
            if (year % 4 == 0)
            {
                if (day > 29)
                    return 0;
            }
            else
            {
                if (day > 28)
                    return 0;
            }
        }

        return 1;
    }
};
int main()
{
    Date date;
    date.input();
    if (date.isValid())
        cout << "Valid date." << endl;
    else
        cout << "Invalid date." << endl;
    return 0;
}
#include<iostream>
using namespace std;
class Student
{
    static int rollNo;
    string name;
    int age;
    string studentClass;
public:
    Student() : name(""), age(0), studentClass("") {}
    void input()
    {
        cout << "Enter name: ";
        cin >> name;
        cout << "Enter age: ";
        cin >> age;
        cout << "Enter class: ";
        cin >> studentClass;
        rollNo++;
    }
    void output()
    {
        cout << "Name: " << name << endl;
        cout << "Age: " << age << endl;
        cout << "Class: " << studentClass << endl;
    }
    static void printTotalStrength()
    {
        cout << "Total Strength: " << rollNo << endl;
    }
};
int Student::rollNo = 0;
int main()
{
    Student s1, s2, s3;
    s1.input();
    s2.input();
    s3.input();
    cout << "\nStudent 1 Details:" << endl;
    s1.output();
    cout << "\nStudent 2 Details:" << endl;
    s2.output();
    cout << "\nStudent 3 Details:" << endl;
    s3.output();
    Student::printTotalStrength();
    return 0;
}