要手工模拟的，不能直接用%.30lf

> #include<stdio.h>
> 
> void main()
> {
> 	long double sum = 0.0,num=0.0;
> 	double k = 0.0;
> 	int  i= 1;
> 	int mod = 10;
> 	int base = 2<<2;
> 
> 	while(scanf("%lf",&num))
> 	{
> 	while(num - int(num)>0.00000001)
> 	{
> 		num = num*10;
> 		k = int(num) %mod;
> 		sum += k/double(base);
> 		base=base<<3;
> 		
> 		k = 0.0;
> 	}
> 	printf("%.30lf\n",sum);
> 	}
> }
> 如何才能保证输出的位数达到要求呢？