How to output the decimal in average?

问题

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

回答1:

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).

回答2:

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.

回答3:

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

回答4:

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

回答5:

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.

来源：https://stackoverflow.com/questions/15799024/how-to-output-the-decimal-in-average

标签

java

while-loop

sum

average

Sentinel