i am a programming enthusiast currently studying for Business Informatics. We have started programming with Java for two months now and i found this website to be of tremendous help in most of the cases i had to write some code for my assignments.
There is however, this assignment for which i have to implement a class that asks a user for a calendar date, validates the date and afterwards calculates and prints the weekday of that date. The program cannot accept dates which do not exist.
The user enters the date in the YYYYMMDD format.
Any impossible date is rejected:
– dates before Oct. 15th 1582 or after Dec, 31st, 2199
– impossible month (<1 or >12)
– impossible day (e.g. any day>31, a day>30 for some months, a day>28 in February of a non-leap year, etc).
We are asked to use the formula derived by Gauss:
A = d + [2.6 x m − 0.2] + y + [y/4]+ [c/4] - (2 x c) W = A % 7
where
[x] is the Gauss-operator: [x] biggest integer x'<= x
d represents the day
y represents the last two digits of the year
c represents the first two digits of the year (actually all but the last two; c stands for century)
m represents the month
w is weekday
We are also asked to implement a few functions to achieve this task. See my code below:
public class Weekdays {
public static void main(String[] args) {
TextIO.putln("enter date (yyyymmdd)");
int date = TextIO.getInt();
int inDay = date % 100, inMonth = date % 10000 / 100, inYear = date / 10000;
if(validate(inYear, inMonth, inDay)){
int W = weekday(inDay, inMonth, inYear);
String weekday = dayName(W);
TextIO.putf("%02d.%02d.%4d was/is or will be a %s", date % 100, date % 10000 / 100,
date / 10000, weekday);
}else {
TextIO.putf("invalid date (%d)\n", date);
}
}
public static boolean validate (int year) {
if (year < 1582 || year > 2199) {
return false;
}
else {
return true;
}
}
public static boolean validate (int year, int month) {
if ((year < 1582 || year > 2199)) {
return false;
}
else if (month < 1 || month > 12) {
return false;
}
else if (year == 1582 && month < 10) {
return false;
}
else {
return true;
}
}
public static boolean isLeap (int inYear) {
return (((inYear % 4 == 0) && (inYear % 400 == 0 || inYear % 100 != 0) ));
}
public static int nDays (int month, int year) {
if ((((year % 4 == 0) && (year % 400 == 0 || year % 100 != 0) ))) {
if (month == 2) {
return 29;
}
else if ((month == 4) || (month == 6) || (month == 9) || (month == 11)) {
return 30;
}
else {
return 31;
}
}
else if (year == 1582 && month == 10) {
return 16;
}
else {
if (month == 2) {
return 28;
}
else if ((month == 4) || (month == 6) || (month == 9) || (month == 11)) {
return 30;
}
else {
return 31;
}
}
}
public static boolean validate (int year, int month, int day) {
if ((year == 1582 && month == 10) && day < 16) {
return false;
}
else if ((year == 1582 && month == 10) && day <= 31) {
}
return (validate(year,month) && day > 0 && day <= nDays(month,year));
}
public static int weekday (int inDay, int inMonth, int inYear) {
int month, year, day,c;
year = inYear;
day = inDay;
if (inMonth < 3) {
year--;
inMonth = inMonth +10;
}
else {
inMonth = inMonth -2;
}
month = inMonth;
c = year/100;
year = year%100;
int A = (int) (day+((2.6*month)-0.2)+year+(year/4)+(c/4)-(2*c));
int x = A % 7;
if (x < 0) {
x+=7;
}
return x;
}
public static String dayName (int W) {
switch (W) {
case 0: return "Sunday";
case 1: return "Monday";
case 2: return "Tuesday";
case 3: return "Wednesday";
case 4: return "Thursday";
case 5: return "Friday";
case 6: return "Saturday";
default: return "invalid date (" +W+ ")";
}
}
}
I have a problem when i am testing two dates, 21010101 and 19190303 respectively. My program outputs wrong weekday's for these two dates. As much as i tried i simply cannot find a way around to it. I know my code is not the best but i am doing what i can as a beginner. Any help would be appreciated. Thank you!
