java使用while、do...while和for循环三种结构计算用户输入的正整数的阶乘

在Java中，可以使用while、do...while和for循环来计算用户输入的正整数的阶乘。以下是三种结构的示例：

1. **while循环**:

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("请输入一个正整数：");
        int num = input.nextInt();

        int factorial = 1;
        while (num > 0) {
            factorial *= num;
            num--;
        }
        System.out.printf("该数字的阶乘是：%d", factorial);
    }
}

2. **do...while循环**:

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int num = 0; // Initialize with a default value to avoid infinite loop on first iteration
        do {
            System.out.print("请输入一个正整数：");
            num = input.nextInt();
            if (num < 0) {
                System.out.println("输入错误，请输入正整数。");
                continue;
            }
            int factorial = 1;
            while (num > 0) {
                factorial *= num;
                num--;
            }
        } while (num <= 0); // Ensure the loop continues until a positive number is entered
        System.out.printf("该数字的阶乘是：%d", factorial);
    }
}

3. **for循环**:

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("请输入一个正整数：");
        int num = input.nextInt();

        if (num < 0) {
            System.out.println("输入错误，请输入正整数。");
        } else {
            int factorial = 1;
            for (int i = 1; i <= num; i++) {
                factorial *= i;
            }
            System.out.printf("该数字的阶乘是：%d", factorial);
        }
    }
}