CodeGym/Help with Java Tasks/Why a mistake?

Level 23

Tyumen

08.05.2019
1854views
7comments

Why a mistake?

Question about the task

Arithmetic mean

Java Syntax, Level 5, Lesson 5

Resolved

Why does an error occur?

package com.codegym.task.task05.task0507;

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Solution {
    public static void main(String[] args) throws Exception {

            int n = 0;
            int count = 0;
            double result;

        for (int i = 1; ; i++) {
            count++;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        int a = Integer.parseInt(reader.readLine());

            if (a != -1){
            n = n + a;
            }

            else if (a == -1){
                result = n/count;
               System.out.println(n);
               break;
            }
            }

    }
}

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; import java.io.BufferedReader; import java.io.InputStreamReader; public class Solution { public static void main(String[] args) throws Exception { int n = 0; int count = 0; double result; for (int i = 1; ; i++) { count++; BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); int a = Integer.parseInt(reader.readLine()); if (a != -1){ n = n + a; } else if (a == -1){ result = n/count; System.out.println(n); break; } } } }

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Greggics

Level 20 , Frankfurt am Main, Germany

8 May 2019, 11:41

result = n/count;

If an Integer gets divided by an Integer, the result will be an Integer. And Integer don't have floating points. In case of a division they will be cut off. So if int n was 10 and int count was 4, then n/count would evaluate to the int value 2, not 2.5. To fix this problem, one the of the both values n or count needs to be double. Because then the expression n/count will evaluate to a double value which allows fractional numbers and will therefore have the expected result.

Serg

Level 23 , Tyumen, Russian

11 May 2019, 15:44

Does not work! Fixed

double n = 0;

an error occurs

If you sequentially enter the numbers 1, 2, 2, 4, 5 and -1, the program should display 2.8.

Really do not understand why this error occurs?

Greggics

Level 20 , Frankfurt am Main, Germany

11 May 2019, 17:57

I noticed that your code increases int count no matter what number is entered for int a. The task says that -1 should not be included in the calculation. Therefore the count must not be increased if a equals -1. So I would put

count++;

inside of the if-branch

if (a != -1){
            n = n + a;
            }

Does that work for you?

Serg

Level 23 , Tyumen, Russian

12 May 2019, 05:18

Сделал так

package com.codegym.task.task05.task0507;

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Solution {
    public static void main(String[] args) throws Exception {

            double n = 0;
            int count = 0;
            double result;

        for (int i = 1; ; i++) {

        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        int a = Integer.parseInt(reader.readLine());

            if (a != -1){
            count++;
            n = n + a;
            }

            else if (a == -1){
               result = n / count;
               System.out.println(n);
               break;
            }
            }

    }
}

Anyway, an old error occurs!

...
If you sequentially enter the numbers 1, 2, 2, 4, 5 and -1, the program should display 2.8.
....
The displayed result should match the task conditions for any input data.

Very interesting to find a solution.

Greggics

Level 20 , Frankfurt am Main, Germany

12 May 2019, 08:37

Oh, I see your program is printing the last number that was entered, double n

System.out.println(n);

but it should print double result instead. What is the output of your program, if you make that change and run the program? I really hope that works, because I honestly can't see what else could be changed after that lol

Djole

Level 41 , Belgrade, Serbia

12 May 2019, 09:47

solution

else if (a == -1){ result = (double)n/count; System.out.println(result); break; }

Serg

Level 23 , Tyumen, Russian

13 May 2019, 05:20

Thank you, friend! Again my inattention how to fix it ...