如何计算 java 中带循环的阶乘

Question

我正在尝试编写一个使用循环计算阶乘的程序的一部分。我没有任何错误消息，但我没有得到任何输出。

是否有针对我的方法的建议，或者是否有使用循环的更好方法？谢谢！

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);
    }
    while (number <= 0);{
        System.out.println("That's not a positive integer!");
    }

    System.out.print(factTotal);
}

}

Answer 1

在您的代码中，在 do...while 循环中，您使用了这个 while 语句：

while (number >= 1);

你没注意到分号吗？这个循环的意义何在？目前它导致无限循环，因为 number 的值永远不会改变，因此你没有得到任何输出。
此外，您的第二个 while 循环应该更像是一个 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);
}

Answer 2

这就是我处理问题的阶乘部分的方法。我会取消 do/while 循环，因为如果你没有得到输出，你就会陷入无限循环。

//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;
}

这就是它在您的代码中的样子。

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 3

@Pernicious，请查看您的程序并稍加修改并添加我的评论。我想这就是你想要做的。

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);
 }
}

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