高精度加法和乘法

[NOIP1998 普及组] 阶乘之和

#include <bits/stdc++.h>
using namespace std;
const int m = 10;
struct ave
{
	int a[5005], len;
	void ass(int x)
	{
		int cnt = 0;
		while(x > 0)
		{
			a[++ cnt] = x % m;
			x /= m;
		}
		len = cnt;
	}
	ave operator * (ave b)
	{
		ave c;
		for (int i = 1; i <= len + b.len; ++ i) c.a[i] = 0;
		for (int i = 1; i <= len; ++ i)
		{
			for (int j = 1; j <= b.len; ++ j)
			{
				c.a[i + j - 1] += a[i] * b.a[j];
				c.a[i + j] += c.a[i + j - 1] / m;
				c.a[i + j - 1] = c.a[i + j - 1] % m;
			}
		}
		if(c.a[len + b.len] != 0) c.len = len + b.len;
		else c.len = len + b.len - 1;
		return c;
	}
	ave operator + (ave b)
	{
		ave c;
		int lenc = max(len, b.len);
		for (int i = 1; i <= lenc + 1; ++ i) c.a[i] = 0;
		for (int i = 1; i <= lenc; ++ i)
		{
			c.a[i] += b.a[i] + a[i];
			c.a[i + 1] += c.a[i] / m;
			c.a[i] %= m;
		}
		if(c.a[lenc + 1] > 0) lenc ++;
		c.len = lenc;
		return c;
 	}
};
ave calc(int n)
{
	ave num, nume;
	num.len = 1, num.a[1] = 1;
	for (int i = 2; i <= n; ++ i)
	{
		nume.ass(i);
		num = num * nume;	
	}	
	return num;
}
int main()
{
	int n;
	scanf("%d", &n);
	ave num;
	num.len = 0, num.a[1] = 0;
	for (int i = 1; i <= n; ++ i) num = num + calc(i);
	for (int i = num.len; i >= 1; -- i) printf("%d", num.a[i]);		
	return 0;
}