如何修复这个无限的while循环

Question

我正在使这个程序能够计算阶乘。如果他们输入超过 20 的值，我需要它说一句话，但我已经创建了无限循环。我的台词说

System.out.print ("ERROR: The result is inaccurate because the number was    too large for the data type");}

是一个无限循环。我似乎无法弄清楚如何解决它。我试过移动东西的位置，但我无法弄清楚。任何帮助表示赞赏。

import java.util.Scanner;
import java.text.NumberFormat;

public class FactoralApp
{
public static void main(String[] arge)
{

    //Welcome users the the application and get user input
    System.out.print("Welcome to the Factoral Calculator" + "\n");


    int num;

    Scanner sc = new Scanner(System.in);
    String choice = "y";
    while (choice.equalsIgnoreCase("y")) {  //set up the while loop so that users can find many factorials

    long factorial=1; //initialize variables


    System.out.print("\n" + "Enter an integer between 1 and 20: "); //promt users for input
    num = sc.nextInt();

    for (int i = num; i >= 1; i--){  //Calculate factorial
    factorial = factorial * i;}

    while (num > 20) {
        System.out.print ("ERROR: The result is inaccurate because the number was too large for the data type");}




    // Format and display the results

    NumberFormat number = NumberFormat.getNumberInstance();

    String message =
                ("\n" + "The factoral of " + num + " is " + number.format(factorial) + "." + "\n"); //create message

    System.out.println(message);  // Output the formated message

    System.out.print ("Continue (y/n): "); //promt users for input
    choice = sc.next();
    } // End While



} // End main ()



} // End Class

Answer 1

我认为你需要一个 if 条件来检查输入的数字是否大于 20，而不是 while。

if(num > 20) {  //the result cannot be stored in a long data type so alert
        System.out.print ("ERROR: The result is inaccurate because the number was too large for the data type");}

// Format and display the results

NumberFormat number = NumberFormat.getNumberInstance();

String message =
            ("\n" + "The factorial of " + num + " is " + number.format(factorial) + "." + "\n"); //create message

System.out.println(message);  // Output the formatted message

System.out.print ("Continue (y/n): "); //prompt users for input
choice = sc.next();
} // End if

Answer 2

我建议你理解控制语句的工作。 while 是一个循环，显然它会一直运行直到满足条件。下面是正确的代码。

public static void main(String[] args) { //Welcome users the the application and get user input
        System.out.print("Welcome to the Factoral Calculator" + "\n");


        int num;

        Scanner sc = new Scanner(System.in);
        String choice = "y";
        while (choice.equalsIgnoreCase("y")) {  //set up the while loop so that users can find many factorials

        long factorial=1; //initialize variables


        System.out.print("\n" + "Enter an integer between 1 and 20: "); //promt users for input
        num = sc.nextInt();

        for (int i = num; i >= 1; i--){  //Calculate factorial
        factorial = factorial * i;}

        if (num > 20) {
            System.out.print ("ERROR: The result is inaccurate because the number was too large for the data type");}




        // Format and display the results

        NumberFormat number = NumberFormat.getNumberInstance();

        String message =
                    ("\n" + "The factoral of " + num + " is " + number.format(factorial) + "." + "\n"); //create message

        System.out.println(message);  // Output the formated message

        System.out.print ("Continue (y/n): "); //promt users for input
        choice = sc.next();
        } // End While



}

说明-：仅以下部分代码已更新。现在上面的代码只会打印一次ERROR: The result is inaccurate because the number was too large for the data type错误。

 if (num > 20) {
            System.out.print ("ERROR: The result is inaccurate because the number was too large for the data type");}   

如果此代码更改不符合您的要求，请提供更多详细信息。您想打印多少次该错误消息。

Answer 3

您永远不会在 while 循环中更改 num 变量的值。由于这是您在 while 循环的布尔条件中检查的变量，因此 条件永远不会改变，并且 while 循环有永远运行的风险。

解决方案：在循环中更新内变量。使用您的 Scanner 变量 sc，就像您在循环之前所做的一样。