I do not get this please help

Question about the task

Arithmetic mean

Java Syntax, Level 5, Lesson 5

Resolved

I have tried many variations with Scanner and now Buffered reader. Any help

Use the keyboard to enter numbers, and then calculate the arithmetic mean.
If the user enters -1, display the arithmetic mean of all entered numbers and end the program.
-1 should not be included in the calculation.

Here are some examples:
a) if you enter the numbers
1
2
2
4
5
-1
then we display
2.8

b) if you enter the numbers
4
3
2
1
-1
then we display
2.5

Hint: one of the solutions to this problem uses the following construct:

while (true) {
    int number = read the number;
    if (check whether the number is -1)
        break;
}

Requirements:

The program must read data from the keyboard.
The program should display data on the screen.
After entering -1, the program must correctly terminate.
If you sequentially enter the numbers 1, 2, 2, 4, 5 and -1, the program should display 2.8.
If you sequentially enter the numbers -100, 0, 100, and -1, the program should display 0.0.
If you sequentially enter the numbers 1 and -1, the program should display 1.0.
The displayed result should match the task conditions for any input data.

package com.codegym.task.task05.task0507; /* Arithmetic mean */ import java.util.Scanner; import java.io.*; public class Solution { public static void main(String[] args) throws Exception { //write your code here int count = 0; int num = 0; int sum = 0; double mean = 0; BufferedReader read = new BufferedReader(new InputStreamReader(System.in)); while (true){ String number = read.readLine(); int num= Integer.parseInt(number); if (num == -1) break; else if (num != -1) sum += num; count++; } mean = sum / count; System.out.println(mean); } }

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horst

Level 26 , Not in list

18 January 2020, 09:30

solution

There is one problem with your calculation that honestly can be a little confusing sometimes. Line 29:

mean = sum / count;

From a human point of view, this looks perfectly fine, but what the computer does here is the following: It takes an integer (sum) and divides it by another integer (count). The result of this division will always be an integer, regardless of whether you store the result in a double afterwards (which you correctly do) or not. So, what your "double mean" variable holds at the moment, is a double representation of an integer division. E.g. sum =5, count = 2, result of 5/2 = 2 (integer division!) double mean = 2.0 (instead of 2.5) To avoid this, make at least one of the variables involved in the division a double. This can be done, for example, by declaring it a double in the first place or - the quick way here - by casting the type like this:

mean = (double) sum / count;

Also, there are some tiny syntax errors in your code that aren't the real problem, but maybe you want to tidy up a little while you're working on it: Line 21:

int num= Integer.parseInt(number);
// The variable "num" has already been declared in line 14, so you don't need the "int" here anymore.

Line 25:

else if (num != -1)

Your else-if statement is the exact opposite of the if-statement, that's why you can simply write "else" without any condition:

else {
    sum += num;
    count++;
}

Pedro Antonio Mendéz Gutiérrez

Level 6 , Crown Point, United States

18 January 2020, 19:06

I cleaned up my code and added the double and it verified. I could not wrap my head over what was wrong. Thank you for the clear explanation!

horst

Level 26 , Not in list

19 January 2020, 21:32

My pleasure. Have fun and all the best for your studies!