15.6—細節實現題—Multiply Strings

描述
Given two numbers represented as strings, return multiplication of the numbers as a string.
Note: e numbers can be arbitrarily large and are non-negative.

#include<iostream>
#include<string>
using namespace std;
string MultiplyString(string s1, string s2)//不考慮非法輸入了。。。
{
	int punctindex1 = 0;
	int punctindex2 = 0;
	int index = 0;
	for (string::iterator it = s1.begin(); it != s1.end(); ++it, index++)
	{
		if (*it == '.')
		{
			s1.erase(it);
			punctindex1 = index;
			break;
		}
	}
	index = 0;
	for (string::iterator it = s2.begin(); it != s2.end(); ++it, index++)
	{
		if (*it == '.')
		{
			s2.erase(it);
			punctindex2 = index;
			break;
		}
	}
	int len1 = s1.size();
	int len2 = s2.size();
	int *p = new int[len1 + len2 + 1];
	for (int i = 0; i <= len1 + len2; i++) p[i] = 0;
	for (int j = len2-1; j >= 0; j--)
	{
		int tmp2 = s2[j] - '0';
		for (int i = len1-1; i >= 0; i--)
		{
			int tmp1 = s1[i] - '0';
			p[i + j + 2] += tmp1*tmp2;
		}
	}
	for (int i = len1 + len2; i >= 1; i--)
	{
		int pre = p[i] / 10;
		p[i] = p[i] % 10;
		p[i - 1] += pre;
	}
	//===
	string res;
	for (int i = 0; i <= len1 + len2; i++)
	{
		char tmp = p[i] + '0';
		res.push_back(tmp);
		//處理小數點情況
		if ((punctindex1 != 0 && punctindex2 != 0) && i == punctindex1 + punctindex2 )//都有小數點
			res.push_back('.');
		if ((punctindex1 != 0 && punctindex2 == 0) && i == punctindex1 + len2)//S1有小數點
			res.push_back('.');
		if ((punctindex1 == 0 && punctindex2 != 0) && i == len1 + punctindex2)//S2有小數點
			res.push_back('.');
	}
	if (res.find('.') == string::npos)
	{
		bool flag = true;
		string result;
		for (int i = 0; i < res.size(); i++)
		{
			if (res[i] == '0'&&flag)
				continue;
			flag = false;
			result.push_back(res[i]);
		}
		return result;
	}
	else
	{
		bool flag = true;
		int nonzerosindex = 0;
		for (int i = 0; i < res.size(); )
		{
			if (res[i] == '0')
				i++;
			else
			{
				nonzerosindex = i; break;
			}
		}
		int punctindex = res.find('.');
		if (nonzerosindex < punctindex)
			return res.substr(nonzerosindex, res.size() - nonzerosindex);
		else
			return res.substr(punctindex - 1, res.size() - punctindex + 1);
	}
}
int main()
{
	string s1 = "10.0003";
	string s2 = "36.00036";
	string res = MultiplyString(s1, s2);
	cout << res << endl;
}