Professor Estrada: Part 2

Statistics.java

package com.saurishsrivastava;
/* name: Saurish Srivastava; strings and loops - part 2:  displays total number of items, average price, and standard deviation of the prices given by user */

/* import used packages */
import java.util.ArrayList;
import java.util.Scanner;

public class Statistics {
    /**
     * Main method
     */
    public static void main(String[] args) {

        /* declare variables and initialize Scanner */
        Scanner input = new Scanner(System.in); // initialize the scanner
        double sinput; // declare sinput double
        int number_items; // declare the number of items variable
        ArrayList<Double> prices = new ArrayList<Double>(); // create an ArrayList for the prices
        double averageprice = 0; // declare the average price variable
        double sd = 0; // declare the standard deviation variable

        System.out.print("Enter first price, or -1 to quit: $"); // prompt user input
        sinput = input.nextDouble(); // assign input to the variable sinput
        prices.add(sinput); // add input to the array list

        if (sinput != -1.0) { // if the input isn't -1 (which means program still runs)
            while (sinput != -1.0) {
                System.out.print("Enter next price, or -1 to quit: $");
                sinput = input.nextDouble();
                prices.add(sinput); // adds all values given by user into array list until -1 is entered
            }
        }
        else {
            System.out.println("Number of items: 0\n" +
                    "No data entered. Cannot calculate statistics.");
            System.exit(0); // stops the program because no data was entered
        }
        prices.remove(prices.size() - 1 ); // get rid of the -1 in the prices array list
        number_items = prices.size(); // assign the number of items to the amount of items in the array

        for(int n = 0; n < prices.size(); n++) {
            averageprice += prices.get(n); // go through all elements and add them to averageprice (so far its a sum)
        }

        averageprice = averageprice/prices.size(); // divide by the size of the array list for the average (sum/items) 

        for (int z = 0; z < prices.size(); z++)
        {
            sd += Math.pow((prices.get(z) - averageprice), 2); // adds all the squares of the difference of prices and means
        }
        sd =  sd / (number_items); // divide by the number of items for the mean
        sd = Math.sqrt(sd); // take the square root

        sd = Math.round(sd*100.0)/100.0; // get standard deviation to two decimal places
        averageprice = Math.round(averageprice*100.0)/100.0; // get average price to two decimal places

        /* ~ Final Results ~ */
        if (number_items == 1) { // if statement for only one item
            System.out.println("Number of items: " + number_items);
            System.out.println("Average price is: $" + averageprice);
            System.out.println("Cannot calculate standard deviation for one item.");
        } else { // for all other statements
            System.out.println("Number of items: " + number_items);
            System.out.println("Average price is: $" + averageprice);
            System.out.println("Standard deviation of prices is $" + sd);
        }
    }
}