How to access an array outside of an if statment? | Together Java | Page 1

wispy tartan Feb 23, 2023, 3:37 AM

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I'm working on a school assignment where a user uses a menu to navigate through different features. One part of the menu has to be where users input data. I'm required to use arrays to store them, but I also need to access them in separate if statements. How can I do that?

steep phoenixBOT Feb 23, 2023, 3:37 AM

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<@&987246399047479336> please have a look, thanks.

steep phoenixBOT Feb 23, 2023, 3:37 AM

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steep phoenix <@&987246399047479336> please have a look, thanks.

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restive dock Feb 23, 2023, 3:38 AM

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declare the array before everything

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share your code so far and I can show you

wispy tartan Feb 23, 2023, 3:40 AM

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public class SortingRectangles {

    @SuppressWarnings("null")
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Welcome to Rectangle Sorter.");
        boolean quit = false;
        while(!quit)
        {
            printMenu();
            int input = keyboard.nextInt();
            int numRectangles = 0;
            double[] rectangleLength;
            double[] rectangleWidth;
            double[] rectangleArea;
            
            if(input==1)
            {
                System.out.println("How many rectangles would you like to sort? Enter a non-zero number");
                numRectangles = keyboard.nextInt();
                while(numRectangles<=0)
                {
                    System.out.println("That is an invalid number. Enter a non-zero number.");
                    numRectangles = keyboard.nextInt();
                }
                
                rectangleLength = new double [numRectangles];
                rectangleWidth = new double [numRectangles];
                rectangleArea = new double [numRectangles];
                
                for(int i = 0;i<numRectangles;i++)
                {
                    System.out.println("Enter the length of rectangle "+(i+1));
                    rectangleLength[i] = keyboard.nextDouble();
                    System.out.println("Enter the width of rectangle "+(i+1));
                    rectangleWidth[i] = keyboard.nextDouble();
                }
                System.out.println("Your data has been succesfully stored.");
                //double[] rectangleArea = new double [numRectangles];
                for(int i = 0;i<numRectangles;i++)
                {
                    rectangleArea[i] = rectangleLength[i]*rectangleWidth[i];
                }
                
            }
            else if(input==2)
            {
                boolean hasSwapped = true;
                while(hasSwapped)
                {
                    hasSwapped = false;
                    for(int i = 0;i<rectangleArea.length-1;i++)
                    {
                        if(rectangleArea[i] > rectangleArea[i+1])
                        {
                            double temp = rectangleArea[i];
                            rectangleArea[i] = rectangleArea[i+1];
                            rectangleArea[i+1] = temp;
                            hasSwapped = true;
                        }
                    }
                }
                System.out.println("The rectangles' areas smallest to largest is:");
                for(int i = 0;i<numRectangles;i++)
                {
                    System.out.println(rectangleArea[i]);
                }
            }
            else if(input==3)
            {
                
            }
            else if(input==4)
            {
                
            }
            else if(input==5)
            {
                
            }
            else if(input==6)
            {
                
            }
            else if(input==7)
            {
                break;
            }
            else if(input<1||input>7)
            {
                System.out.println("Invalid choice.");
            }
        }
        System.out.println("Goodbye!");
        System.exit(0);

    }
    public static void printMenu()
    {
        System.out.println("Enter \"1\" to enter rectangle data.");
        System.out.println("Enter \"2\" to sort rectangle areas from smallest to largest.");
        System.out.println("Enter \"3\" to sort rectangle areas from largest to smallest.");
        System.out.println("Enter \"4\" to show the average rectangle area.");
        System.out.println("Enter \"5\" to show the minimum rectangle area.");
        System.out.println("Enter \"6\" to show the maximum rectangle area.");
        System.out.println("Enter \"7\" to quit the program.");
    }

}```

steep phoenixBOT Feb 23, 2023, 3:40 AM

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wispy tartan ```import java.util.Scanner; public class SortingRectangles { @SuppressWarn...

Detected code, here are some useful tools:

Formatted code

import java.util.Scanner;

public class SortingRectangles {
  @SuppressWarnings("null") public static void main(String[] args) {
    Scanner keyboard = new Scanner(System.in);
    System.out.println("Welcome to Rectangle Sorter.");
    boolean quit = false;
    while (!quit) {
      printMenu();
      int input = keyboard.nextInt();
      int numRectangles = 0;
      double [] rectangleLength;
      double [] rectangleWidth;
      double [] rectangleArea;
      if (input == 1) {
        System.out.println("How many rectangles would you like to sort? Enter a non-zero number");
        numRectangles = keyboard.nextInt();
        while (numRectangles <= 0) {
          System.out.println("That is an invalid number. Enter a non-zero number.");
          numRectangles = keyboard.nextInt();
        }
        rectangleLength = new double [numRectangles] ;
        rectangleWidth = new double [numRectangles] ;
        rectangleArea = new double [numRectangles] ;
        for (int i = 0; i < numRectangles; i++) {
          System.out.println("Enter the length of rectangle " + (i + 1));
          rectangleLength[i]  = keyboard.nextDouble();
          System.out.println("Enter the width of rectangle " + (i + 1));
          rectangleWidth[i]  = keyboard.nextDouble();
        }
        System.out.println("Your data has been succesfully stored.");
        //double[] rectangleArea = new double [numRectangles];
        for (int i = 0; i < numRectangles; i++) {
          rectangleArea[i]  = rectangleLength[i]  * rectangleWidth[i] ;
        }
      }
      else if (input == 2) {
        boolean hasSwapped = true;
        while (hasSwapped) {
          hasSwapped = false;
          for (int i = 0; i < rectangleArea.length - 1; i++) {
            if (rectangleArea[i]  > rectangleArea[i + 1] ) {
              double temp = rectangleArea[i] ;
              rectangleArea[i]  = rectangleArea[i + 1] ;
              rectangleArea[i + 1]  = temp;
              hasSwapped = true;
            }
          }
        }
        System.out.println("The rectangles' areas smallest to largest is:");
        for (int i = 0; i < numRectangles; i++) {
          System.out.println(rectangleArea[i] );
        }
      }
      else if (input == 3) {
      }
      else if (input == 4) {
      }
      else if (input == 5) {
      }
      else if (input == 6) {
      }
      else if (input == 7) {
        break ;
      }
      else if (input < 1 || input > 7) {
        System.out.println("Invalid choice.");
      }
    }
    System.out.println("Goodbye!");
    System.exit(0);
  }
  public static void printMenu() {
    System.out.println("Enter \"1\" to enter rectangle data.");
    System.out.println("Enter \"2\" to sort rectangle areas from smallest to largest.");
    System.out.println("Enter \"3\" to sort rectangle areas from largest to smallest.");
    System.out.println("Enter \"4\" to show the average rectangle area.");
    System.out.println("Enter \"5\" to show the minimum rectangle area.");
    System.out.println("Enter \"6\" to show the maximum rectangle area.");
    System.out.println("Enter \"7\" to quit the program.");
  }
}

wispy tartan Feb 23, 2023, 3:41 AM

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i tried declaring the array above everything but creating the arrays dependent on user input under one of the if statements

restive dock Feb 23, 2023, 3:44 AM

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here

📎 message.txt

steep phoenixBOT Feb 23, 2023, 3:44 AM

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restive dock here

I uploaded your attachments as gist. That way, they are easier to read for everyone, especially mobile users 👍

restive dock Feb 23, 2023, 3:44 AM

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the problem is the in one branch you do not initialize rectangleArea

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so you need to make sure that it is always definitely assigned

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https://javabook.net/variables/delayed_assignment.html

Delayed Assignment - Modern Java

Book teaching how to write modern and effective Java. It is maintained by the community, anyone can contribute.

wispy tartan Feb 23, 2023, 3:46 AM

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thank you!!

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under the second if statement is there any reason the bubble sort would not work?

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@restive dock

restive dock Feb 23, 2023, 4:27 AM

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yes

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you only do one scan

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you need to keep swapping until it is sorted

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also

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you want to move the variable declaration for rectangeArea up higher

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since it will be reset every time through the loop

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                boolean sorted = false;
                while(!sorted)
                {
                    sorted = true;
                    for(int i = 0;i<rectangleArea.length;i++)
                    {
                        if(rectangleArea[i] > rectangleArea[i+1])
                        {
                            double temp = rectangleArea[i];
                            rectangleArea[i] = rectangleArea[i+1];
                            rectangleArea[i+1] = temp;
                            sorted = false;
                        }
                    }
                }

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        int numRectangles = 0;
        double[] rectangleArea = new double[0];

        boolean quit = false;
        while(!quit)
        {
            printMenu();
            int input = keyboard.nextInt();

wispy tartan Feb 23, 2023, 4:36 AM

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thanks again! i found that declaring my rectnagleArea variable further up fixed the problem and that i needed to set the for loop as for(int i = 0;i<rectangleArea.length-1;i++)

#How to access an array outside of an if statment?