C++ 大数乘法

http://acm.buaa.edu.cn/problem/163/

#include <iostream>
#include <cstring>
using namespace std;
#define maxn 2000
char c1[999], c2[999];
int a[999], b[999];
int r[maxn];

void print(int a[], int b[], int la, int lb)
{
	int i, j;
	for(i = 0; i != maxn; i++) r[i] = 0;
	for(i = 0; i != la; i++)
	{
		for(j = 0; j != lb; j++)
		{
			int k = i + j;
			r[k] += a[i] * b[j];
			while(r[k] > 9)
			{
				r[k + 1] += r[k] / 10;
				r[k] %= 10;
				k++;
			}	
		}
	}
	int l = la + lb - 1;
	while(r[i] == 0 && l > 0) l--;
	for(int i = l; i >= 0; i--) cout << r[i];
	cout << endl;
}

int main()
{
	while(cin >> c1 >> c2)
	{
		int la = strlen(c1);
		int lb = strlen(c2);
		for(int i = 0; i != la; i++)
			a[i] = (int)(c1[la - i - 1] - '0');
		for(int i = 0; i != lb; i++)
			b[i] = (int)(c2[lb - i - 1] - '0');
		print(a, b, la, lb);
	}
}