求s=a+aa+aaa+aaaa+aa...a的值，其中a是一个数字。例如2+22+222+2222+22222(此时共有5个数相加)，几个数相加有键盘控制。

1.程序分析：关键是计算出每一项的值。

import java.io.*;
public class Sumloop {
    public static void main(String[] args) throws IOException
    {
        int s=0;
        String output="";
        BufferedReader stadin = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("请输入a的值");
        String input =stadin.readLine();
        for(int i =1;i<=Integer.parseInt(input);i++)
        {
            output+=input;
            int a=Integer.parseInt(output);
            s+=a;
        }
        System.out.println(s);
    }
}

另解:

import java.io.*;
public class Sumloop {
    public static void main(String[] args) throws IOException
    {
        int s=0;
        int n;
        int t=0;
        BufferedReader stadin = new BufferedReader(new InputStreamReader(System.in));
        String input = stadin.readLine();
        n=Integer.parseInt(input);
        for(int i=1;i<=n;i++){
            t=t*10+n;
            s=s+t;
            System.out.println(t);
        }
        System.out.println(s);
    }
}