برنامه ضرب و جمع اعداد بزرگ

#include "stdafx.h"
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
class l_int
{
	vector <int> vec;
protected:
	void fix(l_int & temp)
	{
		if(vec.size()<temp.vec.size())
			for(int i=vec.size();i<temp.vec.size();i++)
				vec.push_back(0);
		else if(vec.size()>temp.vec.size())
			for(int i=temp.vec.size();i<vec.size();i++)
				temp.vec.push_back(0);
	}
	void zero(l_int & temp)
	{
		for(int i=0;i<temp.vec.size();i++)
			temp.vec.at(i)=0;
	}
public:

	l_int(const string txt="0")
	{
		vec.resize(txt.length());
		for(int i=0;i<txt.length();i++)
			vec.at(i)=txt[txt.length()-1-i]-48;
	}
	l_int(l_int &temp )
	{
		/*		
		vec.resize(temp.vec.size());
		for(int i=0;i<temp.vec.size();i++)
		vec.at(i)=temp.vec.at(i);
		*/		
		vec.reserve(temp.vec.size());
		copy(temp.vec.begin(),temp.vec.end(),back_inserter(vec));
	}

	~l_int()
	{
		vec.clear();
	}
	l_int operator + (l_int &temp)
	{
		fix(temp);
		l_int Sum;
		Sum.vec.resize(vec.size());
		zero(Sum);
		int sum=0;
		for(int i=0;i<vec.size();i++)
		{
			Sum.vec.at(i)= ( vec.at(i) + temp.vec.at(i) +sum) %10;
			sum=( vec.at(i) + temp.vec.at(i) +sum ) /10;
			if(i==vec.size()-1 && sum>0)
				Sum.vec.at(vec.size())=sum;
		}
		return Sum;
	}
	l_int operator *(l_int &temp)
	{
		vec.push_back(0);
		temp.vec.push_back(0);
		int sum;
		l_int Mult;
		Mult.vec.resize(temp.vec.size()+vec.size());
		zero(Mult);
		for(int i=0;i<temp.vec.size();i++)
		{
			sum=0;
			for(int j=0;j<vec.size();j++)
			{
				Mult.vec.at(i+j)+=(vec.at(j)*temp.vec.at(i)+sum)%10;
				if(Mult.vec.at(i+j)>9)
				{
					Mult.vec.at(i+j)=Mult.vec.at(i+j)%10;
					Mult.vec.at(i+j+1)++;
				}
				sum=(vec.at(j)*temp.vec.at(i)+sum)/10;
			}
		}
		return Mult;
	}
	l_int& operator =(const l_int &temp)
	{
		vec.resize(temp.vec.size());
		for(int i=0;i<temp.vec.size();i++)
			vec.at(i)=temp.vec.at(i);
		return *this;
	}
	l_int& operator =(const string txt)
	{
		vec.resize(txt.length());
		for(int i = 0 ; i<vec.size() ;i++)
			vec.at(i)=txt[txt.length()-1-i]-48;
		return *this;
	}
	friend ostream& operator <<(ostream &out,l_int &temp);
	friend istream& operator >>(istream &in,l_int &temp);
};
ostream& operator <<(ostream &out,l_int &temp)
{
	bool Check=false;
	for(int i=temp.vec.size()-1;i>=0;i--)
		if(temp.vec.at(i)>0 || Check==true)
		{
			cout<<temp.vec.at(i);
			Check=true;
		}
		if(Check==false)
			cout<<"0";
		return out;
}
istream& operator >>(istream &in,l_int &temp)
{
	string txt;
	cin>>txt;
	temp.vec.resize(txt.length());
	for(int i = 0 ; i<temp.vec.size() ;i++)
		temp.vec.at(i)=txt[txt.length()-1-i]-48;
	return in;
}
int _tmain(int argc, _TCHAR* argv[])
{
	l_int A="20";
	l_int B="10";
	//cin>>A>>B;
	//A="5";
	l_int C;
	l_int D;

	C=A+B;
	D=A*B;
	cout<<"A+B:"<<C<<endl;
	cout<<"A*B:"<<D<<endl;
	system("pause");
	return 0;
}