Case Switch Help?

**xionyus** · October 19th, 2011, 06:13 PM

import java.util.Scanner;
 
public class BirthdayEdit {
 
	public static void main (String arg[])
	{
		Scanner sc = new Scanner(System.in);
 
		int birthMonth = sc.nextInt();
		int birthDay = sc.nextInt();
		int birthYear = (sc.nextInt() - 1900);
		double birthYearRemainder = birthYear % 4;
		int leap;
		int total;
 
		int birthMonthAdd;
		switch (birthMonth) {
			case 1: birthMonthAdd = 1; break;
			case 2: birthMonthAdd = 4; break;
			case 3: birthMonthAdd = 4; break;
			case 4: birthMonthAdd = 0; break;
			case 5: birthMonthAdd = 2; break;
			case 6: birthMonthAdd = 5; break;
			case 7: birthMonthAdd = 0; break;
			case 8: birthMonthAdd = 3; break;
			case 9: birthMonthAdd = 6; break;
			case 10: birthMonthAdd = 1; break;
			case 11: birthMonthAdd = 4; break;
			case 12: birthMonthAdd = 6; break;
		}
		if (birthYearRemainder==0) {
			leap = -1;
		} else {
			leap = 0;
		}
		total = ((birthMonthAdd + birthDay + (birthYear / 4) + birthYear + leap)%7);
		String day;
		if (total == 0) {
		    day = "Saturday";
		} else if (total == 1) {
			day = "Sunday";
			System.out.println("You were born on" + day);
		} else if (total == 2) {
			day = "Monday";
			System.out.println("You were born on" + day);
		} else if (total == 3) {
			day = "Tuesday";
			System.out.println("You were born on" + day);
		} else if (total == 4) {
			day = "Wednesday";
			System.out.println("You were born on" + day);
		} else if (total == 5) {
			day = "Thursday";
			System.out.println("You were born on" + day);
		} else if (total == 6) {
			day = "Friday";
			System.out.println("You were born on" + day);
		} else if (total < 0) {
			System.out.println("An error has occurred.");
		}
    }
}

Trying to design a program that tells you the day you were born. I'm getting this error:

error: variable birthMonthAdd might not have been initialized
total = ((birthMonthAdd + birthDay + (birthYear / 4) + birthYear + leap)%7);

I've tried moving variables around everywhere, but I can't get it to work.

**Tjstretch** · October 19th, 2011, 06:15 PM

Thats a very basic mistake, happens to everyone. Change

int birthMonthAdd;

to

int birthMonthAdd = 0;

It has to do with the compiler not knowing that it will actually get initialized in the switch statement

**xionyus** · October 19th, 2011, 06:57 PM

Originally Posted by Tjstretch

Thats a very basic mistake, happens to everyone. Change

int birthMonthAdd;

to

int birthMonthAdd = 0;

It has to do with the compiler not knowing that it will actually get initialized in the switch statement

Gaah! Thank you so much, it helped me lots. :]
If you're still there I'm wondering if there will be a way to make an error code so that if my teacher types in Feburary 30th, it would give him an error. I really can't think of anything to put for it. That's only if you'd like to help again though. My program works now thanks to you! ;D

import java.util.Scanner;
 
public class BirthdayEdit {
 
	public static void main (String arg[])
	{
		Scanner sc = new Scanner(System.in);
 
		int birthMonth = sc.nextInt();
		int birthDay = sc.nextInt();
		int birthYear = (sc.nextInt() - 1900);
		double birthYearRemainder = birthYear % 4;
		int leap;
		int total;
 
		int birthMonthAdd = 0;
		switch (birthMonth) {
			case 1: birthMonthAdd = 1; break;
			case 2: birthMonthAdd = 4; break;
			case 3: birthMonthAdd = 4; break;
			case 4: birthMonthAdd = 0; break;
			case 5: birthMonthAdd = 2; break;
			case 6: birthMonthAdd = 5; break;
			case 7: birthMonthAdd = 0; break;
			case 8: birthMonthAdd = 3; break;
			case 9: birthMonthAdd = 6; break;
			case 10: birthMonthAdd = 1; break;
			case 11: birthMonthAdd = 4; break;
			case 12: birthMonthAdd = 6; break;
		}
		if (birthYearRemainder==0) {
			leap = -1;
		} else {
			leap = 0;
		}
		total = ((birthMonthAdd + birthDay + (birthYear / 4) + birthYear + leap)%7);
		String day;
		if (birthMonth > 12) {
		System.out.println("Please enter a month number 1-12.");
		} if (birthMonth <= 0) {
		System.out.println("Please enter a month number 1-12.");
		} if (birthYear < 0) {
		System.out.println("The year you entered is earlier than the twentieth century.");
		} if (total == 0) {
		    day = "Saturday";
		    System.out.println("You were born on a " + day);
		} else if (total == 1) {
			day = "Sunday";
			System.out.println("You were born on a " + day);
		} else if (total == 2) {
			day = "Monday";
			System.out.println("You were born on a " + day);
		} else if (total == 3) {
			day = "Tuesday";
			System.out.println("You were born on a " + day);
		} else if (total == 4) {
			day = "Wednesday";
			System.out.println("You were born on a " + day);
		} else if (total == 5) {
			day = "Thursday";
			System.out.println("You were born on a " + day);
		} else if (total == 6) {
			day = "Friday";
			System.out.println("You were born on a " + day);
		} else if (total < 0) {
			System.out.println("An error has occured.");
		}
    }
}

**Tjstretch** · October 19th, 2011, 07:02 PM

You're Welcome, as to your request:

Throwing an error:

throw new AssertionError("Maximum 29 days in Febuary");

Reviewed your code, you should use a switch statement, then use one println. It just looks neater.

It would look like

switch(total)
{
  case 0:
    day = "Saturday";
    break;
  case 1:
    day = "Sunday";
    break;
  case 2:
    day = "Monday";
    break;
  case 3:
    day = "Tuesday";
    break;
  case 4:
    day = "Wednesday";
    break;
  case 5:
    day = "Thursday";
    break;
  case 6:
    day = "Friday";
    break;
  default:
    System.err.println("An error occurred");
    System.exit(0);
}
System.out.println("You were born on a "+day);

Instead of all the else-ifs, however you would have to change

String day;

to

String day = null;

**xionyus** · October 19th, 2011, 07:16 PM

Originally Posted by Tjstretch

You're Welcome, as to your request:

Throwing an error:

throw new AssertionError("Maximum 29 days in Febuary");

Reviewed your code, you should use a switch statement, then use one println. It just looks neater.

It would look like

switch(total)
{
  case 0:
    day = "Saturday";
    break;
  case 1:
    day = "Sunday";
    break;
  case 2:
    day = "Monday";
    break;
  case 3:
    day = "Tuesday";
    break;
  case 4:
    day = "Wednesday";
    break;
  case 5:
    day = "Thursday";
    break;
  case 6:
    day = "Friday";
    break;
  default:
    System.err.println("An error occurred");
    System.exit(0);
}
System.out.println("You were born on a "+day);

Instead of all the else-ifs, however you would have to change

String day;

to

String day = null;

It made my code much more cleaner! Thanks.

One thing can be break the program though.
If I enter a month number over 12, or a negative, then it will still input a day. I know I could fix it with else ifs, but anyway to do it in the way you posted?

**Tjstretch** · October 19th, 2011, 07:27 PM

Oh, thats what you meant. Just use a while statement and an if statement, like so:

int birthMonth = sc.nextInt();
while(birthMonth > 12 || birthMonth < 0)
{
  System.out.println("Invalid birth month, please input a valid number");
  birthMonth = sc.nextInt();
}

However, it would be best to use Integer.valueOf(sc.nextLine()), because sometimes nextInt() causes problems. I find it best just to create a helper method called getInt(sc);, like so:

/**
 * Safely aquires an int from a scanner
 */
private static int getInt(Scanner sc)
{
  int num = Integer.MIN_VALUE;
  while(num == Integer.MIN_VALUE)
  {
    try
    {
      String line = sc.getLine();
      if(line.equalsIgnoreCase("exit");
         System.exit(0);
      num = Integer.valueOf(line);
    }catch(NumberFormatException e)
    {
      System.err.println("Please input a valid number");
    }
  }
}

For getting a valid int, use

int birthMonth = 0;
int birthDay = 0;
int birthYear = 0;
 
while(birthMonth < 1 || birthMonth > 12)
{
  System.out.println("What is your birth month? (Must be between 1 and 12)");
  birthMonth = getInt(sc);
}
//You could use a long switch statement to make sure its right, but I'm going to assume
//the highest value is 31.. you could do it if you want, I'm just to lazy atm.
while(birthDay < 1 || birthDay > 31)
{
  System.out.println("What is your birth day? (Must be between 1 and 31)");
  birthDay = getInt(sc);
}
System.out.println("What is your birth year?");
birthYear = getInt(sc);

**Tjstretch** · October 19th, 2011, 07:32 PM

Sorry if I'm getting over your head, I can break all the code down and explain it if you want

Also, it will make your code look a little less to-the-point, because you have to check everything for validity.

**xionyus** · October 19th, 2011, 07:54 PM

Originally Posted by Tjstretch

Sorry if I'm getting over your head, I can break all the code down and explain it if you want

Also, it will make your code look a little less to-the-point, because you have to check everything for validity.

It's not really over my head, I've been coding and stuff since I was about nine, I learned HTML and CSS from neopets. x3
And I code permissions for MineCraft.
It's just the fact that the first program I created for this same topic worked, but it wasn't what the teacher wanted. He wanted case statements, and I was parsing. I was gone from school for two weeks and his instructions aren't always the best. Just yesterday he was talking about how you have to be "creative" with coding, but nope. I gotta recode my entire program. LOL.
Anyways, I just added a couple of else if statements to the end.

import java.util.Scanner;
 
public class BirthdayEdit {
 
	public static void main (String arg[])
	{
		Scanner sc = new Scanner(System.in);
		int birthMonth = sc.nextInt();
		int birthDay = sc.nextInt();
		int birthYear = (sc.nextInt() - 1900);
		double birthYearRemainder = birthYear % 4;
		int leap;
		int total;
		int birthMonthAdd = 0;
		switch (birthMonth) {
			case 1: birthMonthAdd = 1; break;
			case 2: birthMonthAdd = 4; break;
			case 3: birthMonthAdd = 4; break;
			case 4: birthMonthAdd = 0; break;
			case 5: birthMonthAdd = 2; break;
			case 6: birthMonthAdd = 5; break;
			case 7: birthMonthAdd = 0; break;
			case 8: birthMonthAdd = 3; break;
			case 9: birthMonthAdd = 6; break;
			case 10: birthMonthAdd = 1; break;
			case 11: birthMonthAdd = 4; break;
			case 12: birthMonthAdd = 6; break;
		}
		if (birthYearRemainder==0) {
			leap = -1;
		} else {
			leap = 0;
		}
		total = ((birthMonthAdd + birthDay + (birthYear / 4) + birthYear + leap)%7);
		String day = null;
		switch(total) {
        case 0:
        day = "Saturday";
        break;
        case 1:
        day = "Sunday";
        break;
        case 2:
        day = "Monday";
        break;
        case 3:
        day = "Tuesday";
        break;
        case 4:
        day = "Wednesday";
        break;
        case 5:
        day = "Thursday";
        break;
        case 6:
        day = "Friday";
        break;
        default:
        System.err.println("An error occurred.");
        System.exit(0);
		}
		if(birthMonth > 12 || birthMonth < 0) {
        System.out.println("An error occurred.");
        } else if (birthYear > 101 || birthYear < 1) {
        System.out.println("An error occurred.");
        } else {
        System.out.println("You were born on a " +day);
        }
    }
}

Ended up with that. Works well for me. The only thing that I can't think of a way to counter is if he asks me to put in February 30th.
Also, do you know a way to make the program loop until I put "stop" or something to make the program complete?

**Tjstretch** · October 19th, 2011, 08:00 PM

Ok, 2 things. You should change

int birthMonth = sc.nextInt();
int birthDay = sc.nextInt();
int birthYear = (sc.nextInt() - 1900);

to

System.out.println("What is your birth month?");
int birthMonth = sc.nextInt();
System.out.println("What is your birth day?");
int birthDay = sc.nextInt();
System.out.println("What is your birth year?");
int birthYear = (sc.nextInt() - 1900);

Then, wrap everything after
Scanner sc = new Scanner(System.in)
with a big while statement waiting for a boolean. It's easier to do then explain.
While statements link is here

import java.util.Scanner;
 
public class BirthdayEdit {
 
  public static void main (String arg[])
  {
    Scanner sc = new Scanner(System.in);
    boolean cont = true;
    while(cont)
    {
      System.out.println("What is your birth month?");
      int birthMonth = sc.nextInt();
      System.out.println("What is your birth day?");
      int birthDay = sc.nextInt();
      System.out.println("What is your birth year?");
      int birthYear = (sc.nextInt() - 1900);
      double birthYearRemainder = birthYear % 4;
      int leap;
      int total;
      int birthMonthAdd = 0;
      switch (birthMonth) {
        case 1: birthMonthAdd = 1; break;
        case 2: birthMonthAdd = 4; break;
        case 3: birthMonthAdd = 4; break;
        case 4: birthMonthAdd = 0; break;
        case 5: birthMonthAdd = 2; break;
        case 6: birthMonthAdd = 5; break;
        case 7: birthMonthAdd = 0; break;
        case 8: birthMonthAdd = 3; break;
        case 9: birthMonthAdd = 6; break;
        case 10: birthMonthAdd = 1; break;
        case 11: birthMonthAdd = 4; break;
        case 12: birthMonthAdd = 6; break;
      }
      if (birthYearRemainder==0) {
        leap = -1;
      } else {
        leap = 0;
      }
      total = ((birthMonthAdd + birthDay + (birthYear / 4) + birthYear + leap)%7);
      String day = null;
      switch(total) {
        case 0:
          day = "Saturday";
          break;
        case 1:
          day = "Sunday";
          break;
        case 2:
          day = "Monday";
          break;
        case 3:
          day = "Tuesday";
          break;
        case 4:
          day = "Wednesday";
          break;
        case 5:
          day = "Thursday";
          break;
        case 6:
          day = "Friday";
          break;
        default:
          System.err.println("An error occurred.");
          System.exit(0);
      }
      if(birthMonth > 12 || birthMonth < 0) {
        System.out.println("An error occurred.");
      } else if (birthYear > 101 || birthYear < 1) {
        System.out.println("An error occurred.");
      } else {
        System.out.println("You were born on a " +day);
      }
      System.out.println("Continue?");
      cont = !in.nextLine().equalsIgnoreCase("stop");
    }
  }
}

**Tjstretch** · October 19th, 2011, 08:04 PM

As for checking if its not Febuary 30th, add this with all your other validity checks

else if(birthMonth == 2 && birthDay == 30)
{
  System.out.println("Invalid day!");
  break;
}

**xionyus** · October 19th, 2011, 08:06 PM

Originally Posted by Tjstretch

Ok, 2 things. You should change

int birthMonth = sc.nextInt();
int birthDay = sc.nextInt();
int birthYear = (sc.nextInt() - 1900);

to

System.out.println("What is your birth month?");
int birthMonth = sc.nextInt();
System.out.println("What is your birth day?");
int birthDay = sc.nextInt();
System.out.println("What is your birth year?");
int birthYear = (sc.nextInt() - 1900);

Then, wrap everything after
Scanner sc = new Scanner(System.in)
with a big while statement waiting for a boolean. It's easier to do then explain.
While statements link is here

import java.util.Scanner;
 
public class BirthdayEdit {
 
  public static void main (String arg[])
  {
    Scanner sc = new Scanner(System.in);
    boolean cont = true;
    while(cont)
    {
      System.out.println("What is your birth month?");
      int birthMonth = sc.nextInt();
      System.out.println("What is your birth day?");
      int birthDay = sc.nextInt();
      System.out.println("What is your birth year?");
      int birthYear = (sc.nextInt() - 1900);
      double birthYearRemainder = birthYear % 4;
      int leap;
      int total;
      int birthMonthAdd = 0;
      switch (birthMonth) {
        case 1: birthMonthAdd = 1; break;
        case 2: birthMonthAdd = 4; break;
        case 3: birthMonthAdd = 4; break;
        case 4: birthMonthAdd = 0; break;
        case 5: birthMonthAdd = 2; break;
        case 6: birthMonthAdd = 5; break;
        case 7: birthMonthAdd = 0; break;
        case 8: birthMonthAdd = 3; break;
        case 9: birthMonthAdd = 6; break;
        case 10: birthMonthAdd = 1; break;
        case 11: birthMonthAdd = 4; break;
        case 12: birthMonthAdd = 6; break;
      }
      if (birthYearRemainder==0) {
        leap = -1;
      } else {
        leap = 0;
      }
      total = ((birthMonthAdd + birthDay + (birthYear / 4) + birthYear + leap)%7);
      String day = null;
      switch(total) {
        case 0:
          day = "Saturday";
          break;
        case 1:
          day = "Sunday";
          break;
        case 2:
          day = "Monday";
          break;
        case 3:
          day = "Tuesday";
          break;
        case 4:
          day = "Wednesday";
          break;
        case 5:
          day = "Thursday";
          break;
        case 6:
          day = "Friday";
          break;
        default:
          System.err.println("An error occurred.");
          System.exit(0);
      }
      if(birthMonth > 12 || birthMonth < 0) {
        System.out.println("An error occurred.");
      } else if (birthYear > 101 || birthYear < 1) {
        System.out.println("An error occurred.");
      } else {
        System.out.println("You were born on a " +day);
      }
      System.out.println("Continue?");
      cont = !in.nextLine().equalsIgnoreCase("stop");
    }
  }
}

Thing is, teacher just wanted me to input three numbers like so:
10 20 1990
And when you hit enter it tells you the day you were born.
Would this still be possible to do in a while statement?

**Tjstretch** · October 19th, 2011, 08:11 PM

Yes, it would do that with the above code, except it would ask
"Continue?"
after all that. Run the code and see for yourself

**xionyus** · October 19th, 2011, 08:24 PM

Am I placing the while in the beginning of the program?
If I do it like that, it's giving me multiple errors.

**Tjstretch** · October 19th, 2011, 08:25 PM

I edited the code that I posted, look at how I did it.

**xionyus** · October 19th, 2011, 08:31 PM

I got it working now, but what do I type after Continue pops up?
I'm inputting cont, yes, true, and each just ends the process.
Well, it gives this:

Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Scanner.java:909)
at java.util.Scanner.next(Scanner.java:1530)
at java.util.Scanner.nextInt(Scanner.java:2160)
at java.util.Scanner.nextInt(Scanner.java:2119)
at BirthdayEdit.main(BirthdayEdit.java:14)

**Tjstretch** · October 19th, 2011, 08:57 PM

Hmm thats interesting, one second

**xionyus** · October 19th, 2011, 08:59 PM

import java.util.Scanner;
 
public class BirthdayEdit {
 
	public static void main (String arg[])
	{
		Scanner sc = new Scanner(System.in);
		boolean cont = true;
		while(cont) {
		int birthMonth = sc.nextInt();
		int birthDay = sc.nextInt();
		int birthYear = (sc.nextInt() - 1900);
		double birthYearRemainder = birthYear % 4;
		int leap;
		int total;
		int birthMonthAdd = 0;
		switch (birthMonth) {
			case 1: birthMonthAdd = 1; break;
			case 2: birthMonthAdd = 4; break;
			case 3: birthMonthAdd = 4; break;
			case 4: birthMonthAdd = 0; break;
			case 5: birthMonthAdd = 2; break;
			case 6: birthMonthAdd = 5; break;
			case 7: birthMonthAdd = 0; break;
			case 8: birthMonthAdd = 3; break;
			case 9: birthMonthAdd = 6; break;
			case 10: birthMonthAdd = 1; break;
			case 11: birthMonthAdd = 4; break;
			case 12: birthMonthAdd = 6; break;
		}
		if (birthYearRemainder==0) {
			leap = -1;
		} else {
			leap = 0;
		}
		total = ((birthMonthAdd + birthDay + (birthYear / 4) + birthYear + leap)%7);
		String day = null;
		switch(total) {
        case 0:
        day = "Saturday";
        break;
        case 1:
        day = "Sunday";
        break;
        case 2:
        day = "Monday";
        break;
        case 3:
        day = "Tuesday";
        break;
        case 4:
        day = "Wednesday";
        break;
        case 5:
        day = "Thursday";
        break;
        case 6:
        day = "Friday";
        break;
        default:
        System.err.println("An error occurred.");
        System.exit(0);
		}
		if(birthMonth > 12 || birthMonth < 0) {
        System.out.println("An error occurred.");
        } else if (birthYear > 101 || birthYear < 1) {
        System.out.println("An error occurred.");
        } else if (birthMonth == 2 && birthDay >= 30) {
        System.out.println("An error occurred.");
        } else {
        System.out.println("You were born on a " +day);
        }
        System.out.println("Continue?");
        cont = !sc.nextLine().equalsIgnoreCase("stop");
		}
    }
}

That's my code at the moment.

**Tjstretch** · October 19th, 2011, 08:59 PM

Ok I got it working with:

import java.util.Scanner;
 
public class BirthdayEdit {
 
  public static void main (String arg[])
  {
    Scanner sc = new Scanner(System.in);
    boolean cont = true;
    while(cont)
    {
      System.out.println("What is your birth month?");
      int birthMonth = sc.nextInt();
      System.out.println("What is your birth day?");
      int birthDay = sc.nextInt();
      System.out.println("What is your birth year?");
      int birthYear = (sc.nextInt() - 1900);
      double birthYearRemainder = birthYear % 4;
      int leap;
      int total;
      int birthMonthAdd = 0;
      switch (birthMonth) {
        case 1: birthMonthAdd = 1; break;
        case 2: birthMonthAdd = 4; break;
        case 3: birthMonthAdd = 4; break;
        case 4: birthMonthAdd = 0; break;
        case 5: birthMonthAdd = 2; break;
        case 6: birthMonthAdd = 5; break;
        case 7: birthMonthAdd = 0; break;
        case 8: birthMonthAdd = 3; break;
        case 9: birthMonthAdd = 6; break;
        case 10: birthMonthAdd = 1; break;
        case 11: birthMonthAdd = 4; break;
        case 12: birthMonthAdd = 6; break;
      }
      if (birthYearRemainder==0) {
        leap = -1;
      } else {
        leap = 0;
      }
      total = ((birthMonthAdd + birthDay + (birthYear / 4) + birthYear + leap)%7);
      String day = null;
      switch(total) {
        case 0:
          day = "Saturday";
          break;
        case 1:
          day = "Sunday";
          break;
        case 2:
          day = "Monday";
          break;
        case 3:
          day = "Tuesday";
          break;
        case 4:
          day = "Wednesday";
          break;
        case 5:
          day = "Thursday";
          break;
        case 6:
          day = "Friday";
          break;
        default:
          System.err.println("An error occurred.");
          System.exit(0);
      }
      if(birthMonth > 12 || birthMonth < 0) {
        System.out.println("An error occurred.");
      } else if (birthYear > 101 || birthYear < 1) {
        System.out.println("An error occurred.");
      } else if (birthMonth == 2 && birthDay >= 30) {
        System.out.println("An error occurred.");
      } else {
        System.out.println("You were born on a " +day);
      }
      System.out.println("Continue?");
      sc.nextLine();
      cont = !sc.nextLine().equalsIgnoreCase("no");
    }
  }
}

The problem seems to be that the sc.nextInt() was doing funky stuff again, type no to discontinue

Thread: Case Switch Help?

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Case Switch Help?

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