Question

我试图编写一个程序的一部分，使用循环计算阶乘。我没有任何错误消息，但我没有得到任何输出。

我的方法是否有建议或是否有更好的方法使用循环？谢谢！

FlightInfo

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Answer 1

这是我接近问题的阶乘部分的方式。我会取消do / while循环，因为如果你没有得到输出，你似乎陷入无限循环。

//Call this method when you want to calculate the factorial
public int factorial(int num){
   for(int i = num-1; i > 1; i--){
       num *= i;
   }
   return num;
}

这就是你的代码中的样子。

import java.util.Scanner;

public class Factorial {
public static void main(String[] args) {

    System.out.print("Enter a non-negative number that you wish to perform a factorial function on: ");

    //Create scanner object for reading user input
    Scanner input = new Scanner(System.in);

    //Declare variables
    int number = input.nextInt();
    int factTotal = 1;

    if(number > 0){

        factTotal = factorial(number);

        System.out.print(factTotal);
   }
   else
       System.out.println("This is a negative number");
}

Answer 2

@Pernicious，请稍微修改一下您的程序并添加我的评论。我认为这就是你想要做的事情。

import java.util.Scanner;

public class Factorial {

public static void main(String[] args) {

    System.out.print("Enter a non-negative number that you wish to perform a     factorial function on: ");

    //Create scanner object for reading user input
    Scanner input = new Scanner(System.in);

    //Declare variables
    int number = input.nextInt();
    int factTotal = 1;

// The input number check should be before factorial calculation
    if(number <= 0){
        System.out.println("That's not a positive integer!");
        System.exit(0);
    }

    //Execute factorial
    do {
        factTotal = factTotal * number;
        number--;
// while (number >= 1); This while should be after do{}, not within do{}
    } while (number >= 1);
//        This check should be done immeduately after user input, not after calculation of factorial.
//        while (number <= 0);
//        {
//            System.out.println("That's not a positive integer!");
//        }

    System.out.println(factTotal);
 }
}

Answer 3

在您的代码中，在do...while循环中，您使用了此while语句：

while (number >= 1);

你没注意到分号吗？这个循环有什么意义呢？目前它导致无限循环，因为number的值永远不会改变，因此您没有输出。
另外，你的第二个while循环应该更像是if语句，如下所示那段代码相当于：

while (number >= 1)
{
   //doNothing
}

我相信你的意思是：

import java.util.Scanner;

public class Factorial {
public static void main(String[] args) {

    System.out.print("Enter a non-negative number that you wish to perform a factorial function on: ");

    //Create scanner object for reading user input
    Scanner input = new Scanner(System.in);

    //Declare variables
    int number = input.nextInt();
    int factTotal = 1;

    //Execute factorial
    do{
        factTotal = factTotal * number;
        number--;
    }
    while (number <= 1);
    if(number < 0)
    {
         System.out.println("That is not a positive integer");
    }
    else
    System.out.print(factTotal);
}

如何用java中的循环计算阶乘

3 个答案: