Hi guys, I'm just starting coding and having a heck of a time trying to figure out how to make this application. It's pretty simple and I just want it to input a date, then output a day of the week. If any of you could just give me a few pointers as to where I'm going wrong, I'd greatly appreciate it!

Code:
#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    int startday = 0, sm = 1, sd = 1, sy = 2000, cm = 0, cd = 0, cy = 0;
    cout << "Please enter the current month, day, and year: ";
    cin >> cm >> cd >> cy; int curyear = cy, curmonth = cm, curday = cd;





    //Months added
    while (curmonth >= 1)
    {
        if (curmonth == 1 || 3 || 5 || 7 || 8 || 10 || 12) //March, May, July, August, September, December
        {
            startday = startday + 31;
        }
        else if (curmonth == 2)
        {
            //LEAP YEAR HERE, YOU!
            if ((curyear % 4 == 0) && ((curyear % 400 == 0) || (curyear / 4 != 100)))
            {
                startday = startday + 29;
            }
            else
            {
                startday = startday + 28;
            }
        }
        else if (curmonth == 4 || 6 || 9 || 11)
        {
            startday = startday + 30;
        }
        curmonth--;
    }

    //Years Added
    for (; cy < sy; cy++)
    {
        startday = startday + (365 * cy) + cd;
    }

    int dayname = (startday - 1) % 7;

    if (dayname == 6)
           cout << cm << " " << cd << " " << curyear << " was a Thursday";
    else if (dayname == 0)
           cout << cm << " " << cd << " " << curyear << " was a Friday";
    else if (dayname == 1)
           cout << cm << " " << cd << " " << curyear << " was a Saturday";
    else if (dayname == 2)
           cout << cm << " " << cd << " " << curyear << " was a Sunday";
    else if (dayname == 3)
           cout << cm << " " << cd << " " << curyear << " was a Monday";
    else if (dayname == 4)
           cout << cm << " " << cd << " " << curyear << " was a Tuesday";
    else   cout << cm << " " << cd << " " << curyear << " was a Wednesday";

    return 0;
}