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When the program runs, it asks you to enter a product name and price, and then whenever you press -1 it will be stopped and display a list of the entered product and price. However, the problem is I wrote a selection sort algorithm to sort the list by PRICE in ascending order. The output is not what I expected. Have a look at "//Selection Sort" in this code

import java.util.Scanner;

public class ProductPrices {
    private static Scanner keyboard = new Scanner(System.in);
    private static Scanner key = new Scanner(System.in);

    final static int arrayLength = 1000; //maximum array size
    static float[] productPrice = new float[arrayLength]; //stores the prices of products
    static String[] productName = new String[arrayLength]; //stores the names of products

    public static void main(String[] args) {

        System.out.println("SHOPPING. Press -1 to quit anytime.\n");

        for(int i=0; i<arrayLength; i++) {
            System.out.print("Product: ");
            productName[i] = keyboard.nextLine();
            if(productName[i].equals("-1"))
                break;

            System.out.print("Price: $");
            productPrice[i] = key.nextFloat();
            if(productPrice[i] < 0)
                break;
        }

        System.out.println("\nList of the SHOPPING!\n---------------------");
        for(int i=0; i<productPrice.length; i++) {
            if(productName[i] == null || productName[i].equals("-1") || productPrice[i] < 0)
                continue; // null arrays will not be displayed.
            else {
                // Selection sort
                if(productPrice[i] > productPrice[i+1]) {
                    float temp = productPrice[i];
                    productPrice[i] = productPrice[i+1];
                    productPrice[i+1] = temp;
                }
                System.out.printf("Item: %s %.2f\n", productName[i],  productPrice[i]);
            }
        }
    }
}

    For example
    :::Input:::
    Product: apple
    Price: $2.35
    Product: pie
    Price: $1.36
    Product: cereal
    Price: $7.4
    Product: -1

    :::Output:::
    Item: apple 1.36
    Item: pie 2.35
    Item: cereal 0.00

    That is incorrect, it should be
    Item: pie 1.36
    Item: apple 2.35
    Item: cereal 7.40
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4  
The output is not what I expected. then how is it currently and what do you expect? – Smit May 3 at 16:41
I added the output example in the code there. – Shuvo0o May 3 at 16:54
Well I bet because this will simply throw an ArrayIndexOutOfBoundsException because you're iterating to i<length while accessing [i+1] index. Also even if it did not, all you're doing is switching prices once. So {3,2,1} would become {2,1,3}. See MergeSort for correct, fast and stable sorting. – Marco May 3 at 16:59
I haven't learned MergeSort and I probably shouldn't use it since I was taught to Selection Sort only. – Shuvo0o May 3 at 17:01
I assume its an homework so probably you wont be able to use HashMap either. – Smit May 3 at 17:02
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1 Answer

up vote 0 down vote accepted

Basically you have implemented selection sort incorrectly. Here is the code to fix it, including a counter to count how many products have been entered (makes the implementation clearer). Also as the other post says, you do not swap the names in your example, only the prices. I think the following should work:

public static void main(String[] args) {
    System.out.println("SHOPPING. Press -1 to quit anytime.\n");
    int prodCount = 0;

    for(int i=0; i<arrayLength; i++) {
        System.out.print("Product: ");
        productName[i] = keyboard.nextLine();
        if(productName[i].equals("-1"))
            break;

        System.out.print("Price: $");
        productPrice[i] = key.nextFloat();
        if(productPrice[i] < 0)
            break;

        prodCount++;
    }

    System.out.println("\nList of the SHOPPING!\n---------------------");
    for (int j = 0; j < prodCount-1; j++) {

       int iMin = j;
       for (int i = j+1; i < prodCount; i++) {
           if (productPrice[i] < productPrice[iMin]) {
               iMin = i;
           }
       }
       if ( iMin != j ) {
           float temp = productPrice[j];
           productPrice[j] = productPrice[iMin];
           productPrice[iMin] = temp;
           String tempn = productName[j];
           productName[j] = productName[iMin];
           productName[iMin] = tempn;
       }
    }
    for(int i=0; i<prodCount; i++) {
        System.out.printf("Item: %s %.2f\n", productName[i],  productPrice[i]);
    }
}
share|improve this answer
Its not good to give whole answer. OP is still in learning phase. This way OP wont be able to learn much than copy and paste. – Smit May 3 at 17:26
thanks for the answer but i gotta agree with Smit. you shouldn't give a direct answer. i'm a little confused with prodCount and stuff but I'll try to learn how it works anyway. – Shuvo0o May 3 at 17:43
Yes, on reflection I see what you mean. In any case hopefully you can use this code to help you study how selection sort works. ProdCount counts how many products have been entered, and then is used as the limit for the second loop. So you do not have to loop through all 1000 elements of the array and test for nulls etc. – Matt Hyde May 6 at 8:13

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