Exercise_06_34 Answer!

[SquirrelCoder]

Hey man,

I could not find your answer to Programming Exercise Chapter. 6 Number 34. so I thought I could share my answer :).
PS: Don't know it's efficient, or even a good implementation, but it works pretty good, for any given year.
PS2: I could not find the answer to question No. 33 too, and unfortunately I couldn't solve it yet, though I am working hard on it. When I have written the answer, I will share the code. :)

import java.util.Scanner;

/**
 * Created by SquirrelCoder on 29-Jan-17.
 */
public class ZellerAlgorithm {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        // getting user input
        System.out.print("Enter full year (e.g., 2012): ");
        int year = input.nextInt();
        System.out.print("Enter month as number between 1 and 12: ");
        int month = input.nextInt();

        // check user input
        if (!checkMonth(month)) {
            System.exit(0);
        }

        // print the calendar header
        printCalendarHeader(month, year);

        // print the calendar first day
        printFirstDay(month, year);

        // print the calendar itself
        printCalendarItself(month, year);

    }

    public static int weekDay(int day, int month, int year) {
        if (month == 1 || month == 2) {
            month = month + 12;
            year--;
        }
        int q, m, k, j, h;
        q = day;
        m = month;
        k = year % 100;
        j = (int) (year / 100.0);
        h = (q + (int) ((13 * (m + 1)) / 5.0) + k + (int) (k / 4.0) + (int) (j / 4.0) + (5 * j)) % 7;
        return h;
    }

    public static boolean isLeapYear(int year) {
        return year % 400 == 0 || (year % 4 == 0 && year % 100 != 0);
    }

    public static void printCalendarHeader(int month, int year) {
        switch (month) {
            case 1:
                System.out.print("\t\tJanuary\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 2:
                System.out.print("\t\tFebruary\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 3:
                System.out.print("\t\tMarch\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 4:
                System.out.print("\t\tApril\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 5:
                System.out.print("\t\tMay\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 6:
                System.out.print("\t\tJune\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 7:
                System.out.print("\t\tJuly\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 8:
                System.out.print("\t\tAugust\t");
                System.out.println(year);
                System.out.println("---------------------------");

                break;
            case 9:
                System.out.print("\t\tSeptember\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 10:
                System.out.print("\t\tOctober\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 11:
                System.out.print("\t\tNovember\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;
            case 12:
                System.out.print("\t\tDecember\t");
                System.out.println(year);
                System.out.println("---------------------------");
                break;


        }
        System.out.println("Sun\tMon\tTue\tWed\tThu\tFri\tSat");
    }

    public static int lastDayOfMonth(int month, int year) {
        int lastDayOfMonth;
        if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) {
            lastDayOfMonth = 31;
        } else if (month == 2) {
            if (isLeapYear(year)) {
                lastDayOfMonth = 29;
            } else {
                lastDayOfMonth = 28;
            }
        } else {
            lastDayOfMonth = 30;
        }
        return lastDayOfMonth;
    }

    public static boolean checkMonth(int month) {
        if (month > 12 || month < 0) {
            System.out.println("Invalid Month!");
            return false;
        }
        return true;
    }

    public static void printFirstDay(int month, int year) {
        int firstDay = weekDay(1, month, year);
        switch (firstDay) {
            case 0:
                System.out.print("\t\t\t\t\t\t1");
                break;
            case 1:
                System.out.print("1");
                break;
            case 2:
                System.out.print("\t1");
                break;
            case 3:
                System.out.print("\t\t1");
                break;
            case 4:
                System.out.print("\t\t\t1");
                break;
            case 5:
                System.out.print("\t\t\t\t1");
                break;
            case 6:
                System.out.print("\t\t\t\t\t1");
                break;

        }
        System.out.print("\t");
    }

    public static void printCalendarItself(int month, int year) {

        // find out the last day of that month
        // whether it's 28/29/30/31 days
        int lastDayOfMonth = lastDayOfMonth(month, year);

        // print the calendar itself
        for (int i = 2; i <= lastDayOfMonth; i++) {
            int printedDay = weekDay(i, month, year);
            if (printedDay == 1) {
                System.out.println();
            }
            System.out.print(i + "\t");
        }
    }
}

[jsquared21]

Kool do a pull request and i will accept it.

[SleekPanther]

Not sure what's going on in weekDay. Why do you need to declare duplicate local variables

int q, m, k, j, h;
q = day;
m = month;

why not reuse the parameters? I find the 1-letter variables easy to confuse

printCalendarHeader has a bunch of duplication. You could just make an array of 12 items String[] months = {"January","February","March"}; etc. then loop through it & print the year and "---------------------------" since they're all the same

checkMonth() could probably be shortened & changed to:

public static boolean isValidMonth(int month) {
	return month > 0  &&  month <= 12;
}

(haven't tested though)

printFirstDay could be shortened.
Keep a string with how many tabs required, then loop to keep adding more to the beginning.

String leadingTabs = "1";		//Holds any leading tabs to align 1st row of numbers in a calendar. This takes care of firstDay=1

//cases for firstDay between 2 & 6 (adds a "\t" at the beginning of the string each iteration)
//Loop starts from 1 since we want 1 less tab than the value of firstDay
//(firstDay=1 is 0 tabs, firstDay=2 is 1 tab, firstDay=3 is 2 tabs, firstDay=4 is 3 tabs, firstDay=5 is 4 tabs)
for(int i = 1; i<firstDay; i++){
	leadingTabs = "\t" + leadingTabs;
}
if(firstDay == 0){			//reset it & ignore what the loop did if it's 0. THIS IS A SPECIAL CASE. We want 6 tabs
	leadingTabs = "\t\t\t\t\t\t1";
}

System.out.print(leadingTabs + "\t");

[SquirrelCoder]

Thanks for the reply.
The reason, was, that I did not want to change the formula in the book, this formula is almost identical to the one I used, and I didn't wanted to confuse the variable names. Though, I think I can change that, not a big issue. Thanks for mentioning it.

Yeah I though of Arrays too, but this is the Chapter 6 exercise, and arrays will be introduced in Chapter 7, so for now I don't know, how to use arrays :(. I haven't checked Ch. 7 Exercises, but I am pretty sure, there is one exercise, which wants to re-write this example, using Arrays, though not sure!

checkMonth you are completely correct, I think this works too, the reason I wrote it like that, was, this line: System.out.println("Invalid Month!"); . But I think there is some workaround for this. Will try to work on it. Thanks for mention it.

for the printFirstDay Thanks a lot, will correct it. I greatly appriciate it.

By the way, what's a Pull Request? :D
I just know, how to open a new issue in GitHub, nothing else (pretty new to programming!).

Thanks

[SleekPanther]

Well since checkMonth is a boolean method, you could check its return value when you call it & print the message there instead of just exiting

// check user input
if (!checkMonth(month)) {
    System.out.println("Invalid Month!");
    System.exit(0);
}

I might even suggest doing a while loop to check if the input is invalid & keep asking for a new number until the method return true instead of just exiting

Pull Requests are a not that complicated, but maybe confusing if you don't know git. Basically you Fork someone else's repository, make any changes & commit them on your version, then basically ask the owner of the repository (jsquared21) to accept your changes by pulling them into the main repository
There are some decent tutorials

[SquirrelCoder]

Cool, Thanks a lot man. I greatly appriciate it :).
Will fix the errors.

[jsquared21]

Kool im glad i asked you cause, forking, cloning, pulling and pushing, that is what github is all about. SleekPanther defined the concept well. You should try and learn these concepts and practice them while learning java and working in github. Like SleekPanter said it can be confusing in the beginning but learning them will pay off big time.

[SleekPanther]

@SquirrelCoder I was inspired and ended up making all the edits I mentioned (plus a few more). I was wrong in some of my earlier comments, but you can see the final version in a pull request or check out my actual commit
I made some structural edits (mostly which method comes first is kind of subjective) and I renamed some variables/methods to what I personally think is more helpful

[SquirrelCoder]

Thanks a lot man, I greatly appriciate your commits and your edit. :)

Oh, and I really liked the comments, great idea. Thanks.