C++版大數相乘

#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
using namespace std;

 vector<int> Multiply(string &str1,string &str2)
 {
	 vector<int>vec(str1.size()+str2.size(),0);
	 
	 for(int i = str2.size()-1 , m = 0; i >= 0; i--, m++)
	 {
		 for(int j = str1.size()-1 ,k = 0; j >= 0; j--, k++)
		 {
			 vec[k+m] += (str2[i] - '0')*(str1[j] - '0') ;
		 }
	 }
	 return vec;
 }
 void Dealvector(vector<int>&vec)
 {
	for(int i = 0; i < vec.size(); i++)
	{
		if( vec[i] >= 10)
		{
			vec[i+1] = vec[i+1] + vec[i]/10;
			vec[i] = vec[i] %10;
		}
	}

 }
 string getresult(vector<int>&vec)
 {
	 int len = vec.size()-1;
	 while(vec[len] == 0 && len-- >1)vec.pop_back();
	 vec.shrink_to_fit();
	 string result = "";
	 for_each(vec.rbegin(),vec.rend(),[&](int num)
	 {
		result.append(to_string(num));
	 });
	 return result;
	 
 }
 int main(){
	 string str = "9999"; 
	 string str2 = "9999";
	vector<int> vec( Multiply(str,str2));
	Dealvector(vec);
	string res = getresult(vec);
	 return 0;
 }