header file
_______________:
#include<iostream>
#include<string>

class dayType
{
public:
    void setDay(string day,int num);
    void printDay(string day,int num);
    void returnTheDay(string after);
    void returnNextDay(string day);
    void returnPreviousDay(string day);

private:
    int num;
};

implementation file
________________:
#include<iostream>
#include<string>
#include"day.h"

using namespace std;

void dayType::setDay(string day,int num)
{
    cout<<"Enter a day like 'sunday'/'monday'...etc ";
    cin>>day;
    cout<<endl;
    cout<<"Key in a number of day "
    cin>>num;
    cout<<endl;
}

void dayType::printDay(string day,int num)
{
    cout<<"Today is "<<day<<"after "<<num
        <<"the day is "<<after;
    cout<<endl;

}


void dayType::returnTheDay(string day)
{
    else if (day==sunday)
    {
        return 7;
    }
    else if (day==monday)
    {
        return 1;
    }
    else if (day==tuesday)
    {
        return 2;
    }
    else if (day==wednesday)
    {
        return 3;
    }
    else if (day==thursday)
    {
        return 4;
    }
    else if (day==friday)
    {
        return 5;
    }
    else if (day==saturday)
    {
        return 6;
    }
    
    after=day+num;

    switch(after)
    {
    case '1':
        cout<<"monday";
            cout<<end;
        break;
    case '2':
        cout<<"tuesday";
        cout<<endl;
        break;
    case '3':
        cout<<"wednesday";
        cout<<endl;
        break;
    case '4':
        cout<<"thursday";
        cout<<endl;
        break;
    case '5':
        cout<<"friday";
        cout<<endl;
    case '6':
        cout<<"saturday";
        cout<<endl;
    case '7':
        cout<<"sunday";
        cout<<endl;
    }
}

void dayType::returnNextDay(string day)
{
    if (day==sunday)
    {
        cout<<"The next day is monday ";
        cout<<endl;
    }
    if (day==monday)
    {
        cout<<"The next day is tuesday ";
        cout<<endl;
    }
    if (day==tuesday)
    {
        cout<<"The next day is wednesday ";
        cout<<endl;
    }
    if (day==wednesday)
    {
        cout<<"The next day is thursday ";
        cout<<endl;
    }
    if (day==thursday)
    {
        cout<<"The next day is friday ";
        cout<<endl;
    }
    if (day==friday)
    {
        cout<<"The next day is saturday ";
        cout<<endl;
    }
    if (day==saturday)
    {
        cout<<"The next day is sunday ";
        cout<<endl;
    }
}

void dayType::returnPreviousDay(string day)
{
    if (day==sunday)
    {
        cout<<"The previous day is saturday ";
        cout<<endl;
    }
    if (day==monday)
    {
        cout<<"The previous is sunday ";
        cout<<endl;
    }
    if (day==tuesday)
    {
        cout<<"The previous is monday ";
        cout<<endl;
    }
    if (day==wednesday)
    {
        cout<<"The previous is tuesday ";
        cout<<endl;
    }
    if (day==thursday)
    {
        cout<<"The previous is wednesday ";
        cout<<endl;
    }
    if (day==friday)
    {
        cout<<"The previous is thursday ";
        cout<<endl;
    }
    if (day==saturday)
    {
        cout<<"The next day is friday ";
        cout<<endl;

    }

main program
_____________:
#include<iostream>
#include<string>
#include"day.h"

using namespace std;

void dayType();

int main()

{
    setDay(string day,int num)
        cout<<endl;
    returnTheDay(string after)
        cout<<endl;
    printDay(string day,int num)
        cout<<endl;
    returnNextDay(string name)
        cout<<endl;
    returnPreviousDay(string day)
        cout<<endl;

    return 0;

}

code here

header file:
______________________________________________
enum weekDayType{Sun, Mon, Tue, Wed, Thu, Fri, Sat};

class dayType
{
public:
    void print();
    weekDayType nextDay();
    weekDayType prevDay();
    void addDay(int nDays);

    void setDay(weekDayType d);
    weekDayType getDay();

    dayType();
    dayType(weekDayType d);

private:
    weekDayType weekDay;
};

impletation file:
_______________________________________________
#include <iostream>
#include "dayType.h"

using namespace std;

void dayType::print()
{
    switch(weekDay)
    {
    case Sun: cout<<"Sunday";
              break;
    case Mon: cout<<"Monday";
              break;
    case Tue: cout<<"Tuesday";
              break;
    case Wed: cout<<"Wednesday";
              break;
    case Thu: cout<<"Thursday";
              break;
    case Fri: cout<<"Friday";
              break;
    case Sat: cout<<"Saturday";
    }
}

weekDayType dayType::nextDay()
{
    return weekDayType((weekDay + 1) % 7);
}

weekDayType dayType::prevDay()
{
    if (weekDay == Sun)
        return Sat;
    else
        return weekDayType(weekDay - 1);
}


void dayType::addDay(int nDays)
{
    weekDay = weekDayType((weekDay + nDays) % 7);
}

void dayType::setDay(weekDayType d)
{
    weekDay = d;
}

weekDayType dayType::getDay()
{
    return weekDay;
}

dayType::dayType()
{
    weekDay = Sun;
}

dayType::dayType(weekDayType d)
{
    weekDay = d;
}

main program:
__________________________________________
#include <iostream>
#include "dayType.h"

using namespace std;

int main()
{
    dayType myDay(Mon);
    dayType tempDay;

    cout<<"Today: ";
    myDay.print();
    cout<<endl;

    tempDay.setDay(myDay.nextDay());

    cout<<"Next Day: ";

    tempDay.print();
    cout<<endl;

    tempDay.setDay(myDay.prevDay());

    cout<<"Previous Day: ";

    tempDay.print();
    cout<<endl;

    myDay.addDay(11);
    
    cout<<"After 11 Days: ";
    myDay.print();
    cout<<endl;

    return 0;
}