How to output the decimal in average?

Question

I have a problem in showing the decimals on the average. It keeps showing .00 or .1. I tried to put it in double, but I still get the same results.Also, I want to include the first integer that I input to the sum, but I have no idea how.Please help:

import java.io.*;
import java.util.*;

public class WhileSentinelSum 
{
static final int SENTINEL= -999;

public static void main(String[] args)
{
    // Keyboard Initialization
        Scanner kbin = new Scanner(System.in);

    //Variable Initialization and Declaration
        int number, counter;
        int sum =0;
        int average;

    //Input
        System.out.print("Enter an integer number: " );
        number = kbin.nextInt();
        counter=0;


    //Processing
    //Output
        while(number != SENTINEL)
        {
            counter++;
            System.out.print("Enter an  integer number: ");
            number = kbin.nextInt();
            sum += number;
        }

        if (counter !=0)
            System.out.println("\nCounter is: " + counter);
        else
            System.out.println("no input");

        average= sum/counter;
        System.out.println("The sum is " + sum);
        System.out.println("The average is " + average);


        System.out.println();

    }//end main
}//end class

`average` must be a `double`. At the assignment of average, do this computation: `average = (sum + 0.0)/counter;` — Justin, Apr 03 '13 at 22:07
Check out this: http://stackoverflow.com/questions/2909451/java-simple-division-in-java-bug-feature — Justin, Apr 03 '13 at 22:11

rgettman · Accepted Answer · 2013-04-03T22:19:06.253

5

Even if you declared average to be double, the sum and counter variables are int, so Java still uses integer division before assigning it to average, e.g. 5 / 10 results in 0 instead of 0.5.

Cast one of the variables to double before the division to force a floating point operation:

double average;

...
average = (double) sum / counter;

You can include the first number in your calculation by processing it before you go into the while loop (if it's not the sentinel value).

edited Apr 03 '13 at 22:19

answered Apr 03 '13 at 22:07

rgettman

176,041
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Thank you,how to add the first integer that I input to the sum? – eLg Apr 03 '13 at 22:13
1

The same way you add into the sum in your while loop. – rgettman Apr 03 '13 at 22:14
its giving a different answer – eLg Apr 03 '13 at 22:18
Different as in incorrect? Make sure you _count_ that first number too. – rgettman Apr 03 '13 at 22:21
i did..Enter an integer number: 1 Enter an integer number: 1 Enter an integer number: 1 Enter an integer number: -999 Counter is: 3.0 The sum is -1996.0 The average is -665.3333333333334 – eLg Apr 03 '13 at 22:26
Then you'll have to debug your application to ensure that all 3 ones are being counted and summed, and that the sentinel value _isn't_ being counted and summed. – rgettman Apr 03 '13 at 22:29

arshajii · Answer 2 · 2013-04-03T22:13:38.820

average = sum/counter;

This line is performing integer division (i.e. it cuts off the decimal part of the true result). You should change it to

average = (double) sum / counter;  // perform double division, not int division

which first casts sum as a double and, consequently, performs regular double division.

Note that you will need to change the type of the average variable to double.

Just to illustrate my point:

int a = 3;
int b = 2;

System.out.println(a / b);
System.out.println((double) a / b);

1
1.5

score 1 · Answer 3 · answered Apr 03 '13 at 22:08

1

It looks like the problem is in the line that says

average = sum/counter;

Even if you make average a double, sum/counter is still integer division which will yield an integer answer. You could try saying

double average = ((double)sum)/counter;

Another solution would be to make sum or counter of type double and also make average a double.

answered Apr 03 '13 at 22:08

mottese

192
3
13

Technically speaking, there is no need to enclose `(double) sum` in parentheses... The cast will be applied to _sum_ regardless. That being said, you can make an argument _in favor of_ the parens by saying it's more expressive. – jahroy Apr 03 '13 at 22:15

score 0 · Answer 4 · answered Apr 03 '13 at 22:09

0

Initialize sum and average to double. Use kbin.nextDouble().

answered Apr 03 '13 at 22:09

user2158494

11
3

It's probably better to leave them as ints, but to cast one of them to a double for the division. – jahroy Apr 03 '13 at 22:16

score 0 · Answer 5 · answered Apr 03 '13 at 22:19

0

It is said: Never use double or float, when exact results are needed. You should prefer BigDecimal instead. the primitives don't use a rounding mode most poeple would expect.

answered Apr 03 '13 at 22:19

Mordechai

15,437
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How to output the decimal in average?

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