c++高精度求平方根（保留整数）

#include<iostream>
#include<cstring>
using namespace std;
const int SIZE = 200;
struct hugeint {
	int len, num[SIZE];
};
hugeint times(hugeint a, hugeint b) {
	int i, j;
	hugeint ans;
	memset(ans.num, 0, sizeof(ans.num));
	for (i = 1; i <= a.len; i++)
		for (j = 1; j <= b.len; j++)
			ans.num[i + j - 1] += a.num[i] * b.num[j];
	for (i = 1; i <= a.len + b.len; i++) {
		ans.num[i + 1] += ans.num[i] / 10;
		ans.num[i] %= 10;
	}
	if (ans.num[a.len + b.len] > 0)
		ans.len = a.len + b.len;
	else
		ans.len = a.len + b.len - 1;
	return ans;
}
hugeint add(hugeint a, hugeint b) {
	int i;
	hugeint ans;
	memset(ans.num, 0, sizeof(ans.num));
	if (a.len > b.len)
		ans.len = a.len;
	else
		ans.len = b.len;
	for (i = 1; i <= ans.len; i++) {
		ans.num[i] += a.num[i] + b.num[i] ;
		ans.num[i + 1] += ans.num[i] / 10;
		ans.num[i] %= 10;
	}
	if (ans.num[ans.len + 1] > 0)
		ans.len++;
	return ans;
}
hugeint average(hugeint a, hugeint b) {
	int i;
	hugeint ans;
	ans = add(a, b);
	for (i = ans.len; i >= 2; i--) {
		ans.num[i - 1] += (ans.num[i] % 2) * 10;

		ans.num[i] /= 2;
	}
	ans.num[1] /= 2;
	if (ans.num[ans.len] == 0)
		ans.len--;
	return ans;
}
hugeint plustwo(hugeint a) {
	int i;
	hugeint ans;
	ans = a;
	ans.num[1] += 2;
	i = 1;
	while ((i <= ans.len) && (ans.num[i] >= 10)) {
		ans.num[i + 1] += ans.num[i] / 10;
		ans.num[i] %= 10;
		i++;
	}
	if (ans.num[ans.len + 1] > 0)
		ans.len++;
	return ans;
}
bool over(hugeint a, hugeint b) {
	int i;
	if (a.len < b.len)
		return false;
	if ( a.len > b.len )
		return true;
	for (i = a.len; i >= 1; i--) {
		if (a.num[i] < b.num[i])
			return false;
		if (a.num[i] > b.num[i])
			return true;
	}
	return false;
}
int main() {
	string s;
	int i;
	hugeint target, left, middle, right;
	cin >> s;
	memset(target.num, 0, sizeof(target.num));
	target.len = s.length();
	for (i = 1; i <= target.len; i++)
		target.num[i] = s[target.len - i] - '0';
	memset(left.num, 0, sizeof(left.num));
	left.len = 1;
	left.num[1] = 1;
	right = target;
	do {
		middle = average(left, right);
		if (over(times(middle, middle), target))
			right = middle;
		else
			left = middle;
	} while (!over(plustwo(left), right) );
	for (i = left.len; i >= 1; i--)
		cout << left.num[i];
	return 0;
}