switch statements

I am having a problem understanding switch statements. What I am confused about is where the logic goes. For instance, I created the below problem using if statements. The program verifies whether or not it is true that numbers whose sum of digits is divisible by 3 represent numbers divisible by 3.

Code:

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import java.util.Scanner;

public class ProgrammingProblemTwo {

    public static void main(String[] args) {

            //Create new scanner
            Scanner input = new Scanner(System.in);

            //Ask user to input a five digit number
            System.out.println("Please input a five digit number");
            //create variable number
            int number = input.nextInt();

            //create variable first digit in order to isolate the first digit
            int firstDigit = number / 10000;

            //Create variables a and secondDigit in order to isolate the second digit
            int a = number / 1000;
            int secondDigit = a % 10;

            //Create variables b and thirdDigit in order to isolate the third digit
            int b = number / 100;
            int thirdDigit = b % 10;

            //Create variables c and fourthDigit in order to isolate the fourth digit
            int c = number / 10;
            int fourthDigit = c % 10;

            ////Create variable fifthDigit in order to isolate the fifth digit
            int fifthDigit = number % 10;

            int sum = firstDigit + secondDigit + thirdDigit + fourthDigit +
                    fifthDigit;

            if(number % 3 == 0 && sum % 3 == 0){
                    System.out.println("Both " + number + " and sum " + sum +
                            " are divisible by 3");
            }
                    if(number % 3 != 0 && sum % 3 != 0){
                            System.out.println("Both " + number + " and sum " + sum +
                            " are indivisible by 3");
                    }
                            if(number % 3 == 0 && sum % 3 != 0 || number % 3 != 0 && sum % 3 == 0){
                                    System.out.println("The famous statement is wrong");
                            }
  }
}

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Where I get confused about is where the logic is at in switch statements. For example, here is the code I have so far using the switch statement example in the book:

Code:

---


import java.util.Scanner;

public class ProgrammingProblemTwo {

    public static void main(String[] args) {

            //Create new scanner
            Scanner input = new Scanner(System.in);

            //Ask user to input a five digit number
            System.out.println("Please input a five digit number");
            //create variable number
            int number = input.nextInt();

            //create variable first digit in order to isolate the first digit
            int firstDigit = number / 10000;

            //Create variables a and secondDigit in order to isolate the second digit
            int a = number / 1000;
            int secondDigit = a % 10;

            //Create variables b and thirdDigit in order to isolate the third digit
            int b = number / 100;
            int thirdDigit = b % 10;

            //Create variables c and fourthDigit in order to isolate the fourth digit
            int c = number / 10;
            int fourthDigit = c % 10;

            ////Create variable fifthDigit in order to isolate the fifth digit
            int fifthDigit = number % 10;

            int sum = firstDigit + secondDigit + thirdDigit + fourthDigit +
                    fifthDigit;

        switch (number){

                    case 1: {System.out.println("Both " + number + " and sum " + sum +
                                            " are divisible by 3"); break;}
                    case 2: {System.out.println("Both " + number + " and sum " + sum +
                                            " are indivisible by 3"); break;}
                    case 3: {System.out.println("The famous statement is wrong");break;}
                }
    }
}

---

the syntax information from the book makes no sense to me because all it shows is:

Code:

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switch (expression) {

    case label1: {statements;break;}
    case label2: {statements;break;}
    ...
    ...
    case labelk: {statements;break;}
    default: {statements;break;}
}

---

The book example shows that the statements section is where you add the System.out.println information. It doesn't explain where the logic is at.

Think of switch statements as easier if/else ladders:

Code:

---

swith(value) {
    case ifValueEqualsThis:
        runThisCode();
        break; //if you don't put break here, all code below this will be run too.
    case ifValueEqualsThat:
        runThatCode();
        break;
    ....
    default:
        nothingElseFits();
}

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Quote:

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Originally Posted by ra4king

Think of switch statements as easier if/else ladders:

Code:

---

swith(value) {
    case ifValueEqualsThis:
        runThisCode();
        break; //if you don't put break here, all code below this will be run too.
    case ifValueEqualsThat:
        runThatCode();
        break;
    ....
    default:
        nothingElseFits();
}

---

---

So the logic is part of the case. OK. What if you have two values, such as in this case I have number and sum. I attempted to cut and paste my logic into the case but I get "incompatible types" when I compile it.

Code:

---


switch (sum){

                    case number % 3 == 0 && sum % 3 == 0: {System.out.println(
                            "Both " + number + " and sum " + sum + " are divisible by 3"); break;}
                    case number % 3 != 0 && sum % 3 != 0: {System.out.println(
                            "Both " + number + " and sum " + sum + " are indivisible by 3"); break;}
                    case number % 3 == 0 && sum % 3 != 0 || number % 3 != 0 && sum % 3 == 0:
                            {System.out.println("The famous statement is wrong");break;}

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Please excuse my thick head.

Now you're treating it as a boolean acceptor.
Whenever it runs over each "case" it does if(sum == caseValue).

Quote:

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Originally Posted by ra4king

Now you're treating it as a boolean acceptor.
Whenever it runs over each "case" it does if(sum == caseValue).

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OK, I get it now. It would appear that I can't use a switch statement for this particular problem because the program has to print either "Both number and sum are divisible by 3," "Both n and sum are indivisible by 3," or "The famous statement is wrong." Therefore I have to be able to compare the sum and number variables.

Whatever works and fits your program best :)

Quote:

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Originally Posted by ra4king

Whatever works and fits your program best :)

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Thank you very much for your help. Even though I cannot use a switch statement in this particular program, you helped me understand how to use it.

You're welcome :)