Brain Melting: Trouble With If Statements.....

[UnusualGameBoy]

Haven't been here for a looooooong time.
I'm taking a Java course now...
This is what I gotta do:

"Write an applet to calculate the date following a given date. You will have to take into account leap years. Make sure that your program detects wrong date inputs (ex. month = 13) and displays an error message.

Hint: Create a method that calculates the maximum number of days in a given month.

Months 1, 3,5,7,8,10,12 - have 31 days
Months: 4,6,9,11 - 30 days
Month: 2 - 28 (not a leap year), 29 (leap year)

(use a switch statement to determine maximum number of days)

A leap year is a year that is divisible by 4 except that century years also need to be divisible by 400 to be a leap years

Your output should look something like this:

Enter the month for today's date: 12
Enter the day for today's date: 31
Enter the year for today's date: 1886
Tomorrow's date is 1/1/1887 "

And here is my code:

    private void checkDay(int day, int month, int year){


            switch (month){

               case 1: case 3:  case 5: case 7: case 8: case 10: longMonth(month); break;

               case 2: if ((day>0)&&(day<27)){
                          tday=day++;
                       }else if (day==28){
                          boolean leap =checkLeap(year);
                                 if (leap==true){
                                    tday=1;
                                    tmonth=month++;
                                    tyear=year;
                                 }else if (leap==false){
                                          tday=day++;
                                          tmonth=month;
                                          tyear=year;
                                      }
                       }else if (day==29){
                                tday=day++;
                                tmonth=month;
                                tyear=year;
                       }
                          break;



               case 4: case 6: case 9: case 11: shortMonth (month); break;

               case 12: if ((day>0)&&(day<31)){
                          tday=day++;
                          tmonth=month;
                          tyear=year;
                        }else if (day==31){
                          tday=1;
                          tmonth=1;
                          tyear=year;

                      }

        }//end of switch

    }// end of checkDay

        //Checking Leap Year
        private boolean checkLeap(int year){

            boolean leap;

            if ((year%4==0)&&(year%400==0))
              leap=true;
            else
               leap=false;

           return leap;

        }


        //Long and Short Months
        private void longMonth(int month){

            int tday,tmonth,tyear;

             if ((day>0)&&(day<31)){
                  tday=day++;
                  tmonth=month;
                  tyear=year;
             }else if (day==31){
                  tday=1;
                  tmonth=month++;
                  tyear=year;
             }


        }

         private void shortMonth (int month){

             int tday,tmonth,tyear;

             if ((day>0)&&(day<30)){
                  tday=day++;
                  tmonth=month++;
                  tyear=year;
             }else if (day==30){
                  tday=1;
                  tmonth=month++;
                  tyear=year;
             }

         }

My invocation is:
checkDay(12,31,1886);
g.drawString("Enter the month for today's date: 31",200,400);
g.drawString("Enter the day for today's date: 12", 200,425);
g.drawString("Enter the year for today's date: 1886", 200,450);
g.drawString("Tomorrow's date is "+tday+"/"+tmonth+"/"+tyear,200,475);

I put it in the paint method...

I don't see any mistakes so... I don't really know what to do.
Can anyone help?
Thx.

[UnusualGameBoy]

Sorry for the lack of indentation....
Maybe someone should reprogram the forums to accept them

[sde]

Originally Posted by UnusualGameBoy

Sorry for the lack of indentation....
Maybe someone should reprogram the forums to accept them

lol, ..use [cod e] [/co de] (without the space in the word)

[Belisarius]

Your February check doesn't seem right. You check to see if the day is 29, but don't check to see if it is, in fact, a leap year. Plus, you then go on to increment the day, but I can't think of an instance (apart from old Roman calendars) when February had 30 days.

Further, your leap-year check seems off, as you're checking to see if the year is a multiple of 4 AND 400. Needless to say that 2004, while being a leapyear, isn't a multiple of 400.

For the record, the way that leap-years work is that it's a leap-year every 4 years, except every 100 years, except every 400 years. That's why 1900 and 2100 won't be leap-years, but 2000 was.

Finally, your December check is off, as you set the next year to the current year. Hence, 12/31/04 will turn into 1/1/04.

Those are the mistakes I see off the top of my head. But, you didn't mention what was actually going wrong, so I'm not sure if I answered your question or not.