Problem #19

Ok, first thing about solving this is that, since we are going from 1901 - 2000, we dont have to worry about any special leap year conditions, just that it is a leap year every year divisible by four (1904, 1908, 1912, ..., 2000).

I avoided doing this one for a while because I thought it would be hard...heres the code I wrote for it, solved it correctly on my first try.

#include <iostream>
#include <string>

using namespace std;

int daysPerMonth (int, int);
void addOneDay (string&);

int main()
{
    string day = "Monday";
    int total = 0;

    for (unsigned int i = 1901; i < 2001; i++)
        for (unsigned int j = 1; j <= 12; j++)
            for (unsigned int k = 1; k <= static_cast<unsigned int> (daysPerMonth (j, i)); k++)
            {
                addOneDay (day);
                if (k == 1 && day == "Sunday")
                    total++;
            }

    cout << total << endl;
    
    system ("pause");
    return 0;
}

// Returns the number of days in that month. If the month is february, it returns
// 29 iff the year is divisible by four
int daysPerMonth (int month, int year)
{
    switch (month)
    {
    case 1:// Jan
        return 31;

    case 2:// Feb
        if (year % 4 == 0)
            return 29;
        return 28;

    case 3:// March
        return 31;

    case 4:// April
        return 30;

    case 5:// May
        return 31;

    case 6:// June
        return 30;

    case 7:// July
        return 31;

    case 8:// August
        return 31;

    case 9:// Sep
        return 30;

    case 10:// Oct
        return 31;

    case 11:// Nov
        return 30;

    case 12:// Dec
        return 31;

    default:// Error
        return 0;

    }
}

void addOneDay (string &day)
{
    if (day == "Sunday")
        day = "Monday";
    else if (day == "Monday")
        day = "Tuesday";
    else if (day == "Tuesday")
        day = "Wednesday";
    else if (day == "Wednesday")
        day = "Thursday";
    else if (day == "Thursday")
        day = "Friday";
    else if (day == "Friday")
        day = "Saturday";
    else if (day == "Saturday")
        day = "Sunday";
}