用 do…..while, while, for 三种循环语句求 n!(要求 n 的值从键盘输入), 输出结果。

以下是三种循环语句求n!的例子，其中n的值从键盘输入：
1.使用do...while循环语句

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int result = 1;        int i = 1;
        do {
            result *= i;
            i++;
        } while (i <= n);
        System.out.println(n + "! = " + result);
    }
}

2.使用while循环语句

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int result = 1;        int i = 1;
        while (i <= n) {
            result *= i;
            i++;
        }
        System.out.println(n + "! = " + result);
    }
}

3.使用for循环语句

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int result = 1;        for (int i = 1; i <= n; i++) {
            result *= i;
        }
        System.out.println(n + "! = " + result);
    }
}