求2+22+222+2222+.....的N项之和

<span style="font-size:18px;">import java.util.Scanner;public class SumDemo3 {public static void main(String[] args) {// 求2+22+222+2222+.....for (;;) {Scanner scanner = new Scanner(System.in);System.out.println("请输入1到8表示项数");int n = scanner.nextInt();int s = 0; //总和int item = 0; //其中一个变量int a = 2;for (int i = 1; i <= n; i++) {item = item * 10 + a;s = s + item;}System.out.println("你输出的和为："+s);}}}</span>

思路：找到变化规律把它设为item,然后把它套用到s=s+item公式用。