没有输入正数时如何显示正确的输出

Question

I'm new to coding. Assignment is to calculate the average of all the positive numbers input and exit when a zero is input. If no positive numbers are input display a message average not possible.

The following is what I have so far. I am stuck on the part about printing out the message "cannot calculate the average" when only a zero or negative numbers are input.

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int numbers = 0;
    int sumOfNumbers = 0;
    double averagePositive = 0;
    while (true) {
        System.out.println("Give a number: ");
        int number = Integer.valueOf(scanner.nextLine());
        if (number == 0)
            break;

        if (number > 0)
            sumOfNumbers = number + sumOfNumbers;

        if (number > 0)
            numbers = numbers + 1;

        if (number > 0)
            averagePositive = (double)sumOfNumbers / (double)numbers;
    }   
    System.out.println(averagePositive);
}

Answer 1

Try it as follows...

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);

    System.out.print("Give a number: ");
    int num=input.nextInt();
    int tot=0; //total
    int count=0; // counting the positive numbers
    if(num>0){
         while(num!=0){
             tot+=num;
             count++;
             System.out.print("Give a number: ");
             num=input.nextInt();
             if(num<0){
              System.out.print("Not possible");
              return;
              }
         }
         double avg =(double)tot/n;
         System.out.print("Average: "+avg);

    }else{
         System.out.println("Cannot calculate the average.");
    }

}

Answer 2

I'd probably do it like this to keep it simple. Also in general, try not to cramp code together. Most formal project demand a certain degree of styling and usually spaces between operators and braces, etc... is required. In the long run it makes the code more readable and easier to maintain.

In your code there was no need to repeat the same if test for number > 0 multiple times, they could have all been bundled together. If the program was bigger and more complex I may have named the variable names with more qualification but for a short program like this, brief names were sufficient for clarity.

continue and break are important keywords to control loop behavior and can be used to increase brevity and clarity. continue goes back to the top of the loop immediately and break exits the innermost loop immediately. Dividing a double by an int yields a double so I was able to eliminate a cast. And the += operator makes it a little easier to read the line.

Also in Java and C any if() or else clause that contains one line doesn't require braces and unless a program is nested in such a way that adding the braces anyway adds to the clarity, it is often clearer to omit the braces in that case. The if statement illustrates both ways in a single statement.

import java.util.Scanner;
public class avg 
{
    static int count = 0;
    static double sum = 0;

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        System.out.println("\nEnter a sequence of positive numbers (0 to calculate average):\n");

        while (true) {
            System.out.print("Number? ");
            int n = scanner.nextInt();
            if (n < 0) {
                System.out.println("Negative numbers not allowed.");
                continue;
            } else if (n == 0)
                break;

            sum += (double)n;
            ++count;
        }           

        System.out.println("Average of " + count + " numbers = " + 
            (double)(sum / count) + "\n");


        System.exit(1);
    }
}

Sample output:

$ java avg

    Enter a sequence of positive numbers (0 to calculate average)

    Number? 1
    Number? 2
    Number? 3
    Number? 4
    Number? 5
    Number? -6
    Negative numbers not allowed.
    Number? 0

    Average of 5 numbers = 3.0

Answer 3

I'm new to coding. Assignment is to calculate the average of all the positive numbers input and exit when a zero is input. If no positive numbers are input display a message average not possible.

The following is what I have so far. I am stuck on the part about printing out the message "cannot calculate the average" when only a zero or negative numbers are input.

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int numbers = 0;
    int sumOfNumbers = 0;
    double averagePositive = 0;
    while (true) {
        System.out.println("Give a number: ");
        int number = Integer.valueOf(scanner.nextLine());
        if (number == 0)
            break;

        if (number > 0)
            sumOfNumbers = number + sumOfNumbers;

        if (number > 0)
            numbers = numbers + 1;

        if (number > 0)
            averagePositive = (double)sumOfNumbers / (double)numbers;
    }   
    System.out.println(averagePositive);
}