用while循环的，有点复杂

S=2+22+222+2222.....

大佬帮帮我

import java.util.Scanner;
public class Demo {
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);
        System.out.println("输入整数a:");
        int a=in.nextInt();
        int sum=0,num=a,n=1;
        String str=a+"";
        while (n<=num)
        {
            sum+=a;
            a=(a*10)+num;
            if (n<num){
                str=str+"+"+a;
            }
            n++;
        }
        System.out.print("s="+str+"="+sum);
    }
}

#include<stdio.h>

    int main(){
    int a,n,s;
    int i=0;
    scanf("%d%d",&a,&n);
    while(i<=n) {
        s += a + pow(10,i);
        i++;
    }
    printf("%d",s);
    return 0;
}