java使用dowhile循环创建一个Averager

Question

该程序必须提示用户输入一个正数，如果不输入，则只在用户输入-1时结束。我遇到的问题是，在用户输入负数并且程序继续运行后，如何计算实际平均值。它会在不应该的情况下计算负数。即使用户输入负数，我如何让它打印出正确的平均值

package averager;

import java.util.Scanner;

public class Averager {

    public static void main(String[] args) {
        double sum = 0; // use for storing addition to all entered values..
        double num, count = 0;
        Scanner scan = new Scanner(System.in);

        do {

            System.out.print("Enter any positive number, enter -1 to quit: ");
            num = scan.nextDouble();
            sum = sum + num;
            count++;

            if (num <= 0) {
                System.out.println("Please enter a positive number.");

            } else if (num != -1) {
                System.out.println("Average is : " + sum + "/" + count + " = " + (sum / count));
            } else if (num == -1) {
                System.out.println("Average is : " + (sum + 1) + "/" + (count - 1) + " = " + ((sum + 1) / (count - 1)));


            }

        } while (num != -1);

    }

}

Answer 1

这是一个使用printf（而不是进行String串联）的好地方。你对使用do-while的要求使它比其他方法更复杂，但逻辑测试是num != -1；可以使用continue跳过负值/零值。比如

double sum = 0, num = 0;
int count = 0;
Scanner scan = new Scanner(System.in);
do {
    System.out.print("Enter any positive number, enter -1 to quit: ");
    num = scan.nextDouble();
    if (num != -1) {
        if (num <= 0) {
            System.out.println("Please enter a positive number.");
            continue;
        }
        sum += num;
        count++;
    }
} while (num != -1);
System.out.printf("Average is : %.2f/%d = %.2f%n", sum, count, sum / count);

Answer 2

逻辑中的问题是，在接受输入和将其添加到计算中之前，需要评估输入

比如：

import java.util.Scanner;

public class Averager {

    public static void main(String[] args) {
        double sum = 0, num, count=0;
        Scanner scan = new Scanner(System.in);

        System.out.print("Enter any positive number, enter -1 to quit: ");

       do{  
          num = scan.nextDouble(); // get the input
          if(num==-1){// is it -1?          
             if(sum>0){// if yes check if there is any previous input 
               System.out.println("Average is :" + 
                                 sum + "/" + count + " = " + (sum / count));
             }
             else {
                   System.out.println("You chose to terminate the program");
              }
              break; // break the loop 
           }
           else if(num<=0){ // if it's invalid input, inform the user
                System.out.println("Please enter a positive number. Try again:");
           }
           else{// the program will reach this point if everything is ok
                // and if the user hasn't terminated the program yet
               sum +=num; // add the number 
               count++; // increment the counter
           }    
        } while(true); // this will break only when user inputs -1
        scan.close();
    }
}

Test1

Enter any positive number, enter -1 to quit: -1
You chose to terminate the program

Test2

Enter any positive number, enter -1 to quit: -5
Please enter a positive number. Try again:
1
2
3
-1
Average is : 6.0/3.0 = 2.0