編程實現．求Sn=a+aa+aaa+.......+aaa....aaa之值，其中a是壹個數字，n表示a的位數，例：2＋22＋222＋2222

#include "math.h"

void main()

{ int a,n,i;

long sum=0;

printf("Please input a(0<a<=9) and n:");

scanf("%d%d",&a,&n);

if(a>9||a<=0)

{

printf("a is not in (1,2,3,4,5,6,7,8,9)!\nplease input a again:");

scanf("%d",&a);

}

for(i=1;i<=n;i++)

{

sum+=(pow(10,i)-1)*a/9.0;

}

printf("sum=:%ld",sum);

}