a+aa+aaa+++++++aaaaaaaaaaa(n个)怎么用c++编

#include "stdio.h"
#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);

}

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运行已经通过，aa.....aa的长度增长！！！！

main()
{
printf("%d",sum(2,3));
}
int sum(int a,int n)
{
int i,b=0,s=0;
for(i=0;i<n;i++)
{
b=b*10+a;
s+=b;
}
return s;
}