阶乘计算器

Question

我如何使程序执行一个新的或重复的操作，或要求用户再次输入一个数字，并知道它的阶乘。

import java.util.Scanner;

public class Loops {

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

        int num, num2 = 1, x, i;

        System.out.println("-------------Factorial Calculator-------------");
        System.out.print("Enter a positive integer: ");
        num = input.nextInt();

        if (num > 0) {
            System.out.print(num + "! = ");
            for (i = 1; i <= num; i++) {
                if(i < num){
                    System.out.print(i + " x ");
                    num2 = num2 * i;
                }
                if(i == num){
                    System.out.print(i);
                    num2 = num2 * i;
                    System.out.println("\nThe factorial of " + num + " is " + num2);
                    System.out.println();
                }
            }
        }else if (num < 0) {
            System.out.println("Please input a valid integer. Program stopped.");
        }
    }
}

Answer 1

将计算阶乘的代码放在单独的方法中，并从main()中的循环中调用它。

import java.util.Scanner;

public class Loops {

    public static void printFactorial(int num) {
        int i = 0;
        int num2 = 0;
        if (num > 0) {
            System.out.print(num + "! = ");
            for (i = 1; i <= num; i++) {
                if(i < num){
                    System.out.print(i + " x ");
                    num2 = num2 * i;
                }
                if(i == num){
                    System.out.print(i);
                    num2 = num2 * i;
                    System.out.println("\nThe factorial of " + num + " is " + num2);
                    System.out.println();
                }
            }
        }else if (num < 0) {
            System.out.println("Please input a valid integer. Program stopped.");
            System.exit(0);
        }

    }
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        int num = 0;
        System.out.println("-------------Factorial Calculator-------------");
        while ( true ) {
            System.out.print("Enter a positive integer: ");
            num = input.nextInt();
            printFactorial(num);
        }
    }
}

Answer 2

使用while循环

import java.util.Scanner;

public class Loops {
    static boolean readInput = true;
    public static void main(String[] args) {
        while(readInput) calculateFactorial();
    }
}

private static void calculateFactorial() {
    Scanner input = new Scanner(System.in);

    int num, num2 = 1, x, i;

    System.out.println("-------------Factorial Calculator-------------");
    System.out.print("Enter a positive integer: ");
    num = input.nextInt();
    if(num <= 0) {
        readInput = false;
        return;
    }

    if (num > 0) {
        System.out.print(num + "! = ");
        for (i = 1; i <= num; i++) {
            if(i < num){
                System.out.print(i + " x ");
                num2 = num2 * i;
            }
            if(i == num){
                System.out.print(i);
                num2 = num2 * i;
                System.out.println("\nThe factorial of " + num + " is " + num2);
                System.out.println();
            }
        }
    }else if (num < 0) {
        System.out.println("Please input a valid integer. Program stopped.");
    }
}

Answer 3

当用户不键入位置号时，请使用when循环：

System.out.print("Enter a positive integer: ");
num = input.nextInt();
while(num<0) {
    System.out.println("Please input a valid integer. Program stopped.");
    num = input.nextInt();
}

代码:

    import java.util.Scanner;

public class Main {

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

        int num, num2 = 1, x, i;

        System.out.println("-------------Factorial Calculator-------------");
        System.out.print("Enter a positive integer: ");
        num = input.nextInt();
        input.nextLine();
        while (num < 0) {
            System.out.println("Please input a valid integer. Program stopped.");
            System.out.print("Enter a positive integer: ");
            num = input.nextInt();
        }
        if (num > 0) {
            System.out.print(num + "! = ");
            for (i = 1; i <= num; i++) {
                if (i < num) {
                    System.out.print(i + " x ");
                    num2 = num2 * i;
                }
                if (i == num) {
                    System.out.print(i);
                    num2 = num2 * i;
                    System.out.println("\nThe factorial of " + num + " is " + num2);
                    System.out.println();
                }
            }
        }
    }
}