c++的高精

python自带高精，Java也有BigInteger和BigDecimal类，c++。。。

#include <bits/stdc++.h>
using namespace std;

class BigInteger {
public:
	//获取snum字符串，setup()转换成数组
	string snum = "";
	vector<size_t> num;

	//构造器，定义vector大小。。
	BigInteger() {
		num.resize(40000);
	}

	void setup() {
		//为了思考方便些，把数字颠倒过来。。
		std::reverse(snum.begin(), snum.end());
		for (int i = 0, l = snum.length(); i < l; ++i)
			num[i] = snum[i] - '0';
		return;
	}

	//相加，直接在这个对象上面加
	string add(BigInteger b) {
		if (snum == "0") return b.snum;
		if (b.snum == "0") return snum;

		//用stringstream记录每次相加的过程
		stringstream ss;
		for (int i = 0, l = max(snum.length(), b.snum.length()); i <= l; ++i) {
			num[i] += b.num[i];
			//其实直接第一个++，第二个-=10就行
			if (num[i] > 9) {
				num[i + 1] += num[i] / 10;
				num[i] = num[i] % 10;
			}
			ss << num[i];
		}

		//直接转成字符串颠倒去头部0输出
		string s = ss.str();
		std::reverse(s.begin(), s.end());

		int i = 0;
		for (int l = s.length(); i < l; ++i)
			if (s[i] != '0') break;

		return s.substr(i);
	}

	string times(BigInteger b) {
		//跟上面差不多，如果是0返回0，如果是1返回另外一个
		if (snum == "0" || b.snum == "0") return "0";
		if (snum == "1") return b.snum;
		if (b.snum == "1") return snum;

		//这里用的是另外一个temp对象来储存..
		BigInteger temp;
		//还是用stringstream储存输出
		stringstream ss;

		for (int i = 0, l1 = snum.length(); i <= l1; ++i) {
			for (int j = 0, l2 = b.snum.length(); j <= l2; ++j) {
				temp.num[i + j] += num[i] * b.num[j];
				if (temp.num[i + j] > 9) {
					temp.num[i + j + 1] += temp.num[i + j] / 10;
					temp.num[i + j] = temp.num[i + j] % 10;
				}
			}
		}

		for (int i = 0, l = temp.num.size(); i < l; ++i)
			ss << temp.num[i];

		string s = ss.str();
		std::reverse(s.begin(), s.end());

		int i = 0;
		for (int l = s.length(); i < l; ++i)
			if (s[i] != '0') break;

		return s.substr(i);
	}
};

int main() {

	//Add
	/*BigInteger i1, i2;
	cin >> i1.snum >> i2.snum;

	i1.setup();
	i2.setup();

	cout << i1.add(i2);*/

	//Multiply
	BigInteger b1, b2;
	cin >> b1.snum >> b2.snum;

	b1.setup();
	b2.setup();

	cout << b1.times(b2);
	return 0;
}

这里只有加和乘，剩下的还没写

测试一下乘法：

In：

999999999999999999999999999999

233336666699990000651919556666

Out:

233336666699990000651919556665766663333300009999348080443334

跟python算的一样没错

还有加法：

In:

999999999999999999999999999999

233336666699990000651919556666

Out:

1233336666699990000651919556665

一样+1