C++中的大数乘的实现

代码

来源：面试常考 大数加减乘除

#include <iostream>
#include <vector>
#include <string>

using namespace std;

vector<int> mult(string s1, string s2)
{
	int l1 = s1.size();
	int l2 = s2.size();
	vector<int> res(l1 + l2, 0);
	for (int i = 0; i < l1; i++)
	{
		for (int j = 0; j < l2; j++)
		{
			res[i + j + 1] += ((s1[i] - '0')*(s2[j] - '0'));
		}
	}
	int x = l1 + l2 - 1;
	for (int i = x; i > 0; i--)
	{
		res[i - 1] += res[i] / 10;
		res[i] %= 10;
	}
	return res;
}

int main()
{
	string a = "99999";
	string b = "99999";
	vector<int> ans = mult(a, b);
	int i = 0;
    //去除前面的0
	while (i < ans.size() && ans[i] == 0)
	{
		i++;
	}
	for (; i < ans.size(); i++)
	{
		cout << ans[i];
	}
	cout << endl;
	system("pause");
	return 0;
}