Big Number Calculation

BigNumberCalculation.cpp

//Big Number Calculation
//You can Add, Subtract or Multiply a BigNumber.
//What's more, all the calculations are done in base 10000 system. SPEED UP!!!
//You can adjust base system by changing NUM_PER_BIT and NUM_PER_BIT_BIT.

#include<iostream>
#include<sstream>
#include<iomanip>
#include<string>
#include<cstring>

using namespace std;

const int MAX_BITS=1000;
const int NUM_PER_BIT=10000;
const int NUM_PER_BIT_BIT=4;

class Tool
{
public:
	static int toInt(string s)
	{
		int tmp=0;

		for(int i=0;i<s.size();i++)
		{
			tmp=tmp*10+int(s[i]-'0');
		}

		return tmp;
	}
};

class Number
{
public:
	int bits;
	int n[MAX_BITS];
	bool symbol;

	Number()
	{
		symbol=true;
		bits=1;
		memset(n,0,sizeof(n));
	}
	~Number()
	{
	}

	int fromString(string s)
	{
		string tmp;
		memset(n,0,sizeof(n));
		bits=0;
		for(int i=s.size()-1;i>=0;i-=NUM_PER_BIT_BIT)
		{
			int tmpSize=NUM_PER_BIT_BIT;
			int tmpI=i-NUM_PER_BIT_BIT+1;
			if(tmpI<0)
			{
				tmpI=0;
				tmpSize=i+1;
			}
			tmp=s.substr(tmpI,tmpSize);
			n[bits++]=Tool::toInt(tmp);
		}
		Settle();
		return 0;
	}

	string toString()
	{
		stringstream stream;
		for(int i=bits-1;i>=0;i--)
		{
			if(i!=bits-1)
			{
				stream<<setw(NUM_PER_BIT_BIT)<<setfill('0')<<n[i];
			}
			else
			{
				stream<<n[i];
			}
		}
		string tmp;
		stream >>tmp;
		if(symbol==false)
		{
			tmp="-"+tmp;
		}
		return tmp;
	}

	void Settle()
	{
		for(int i=MAX_BITS-1;i>=0;i--)
		{
			if(n[i]!=0)
			{
				bits=i+1;
				return;
			}
		}
		bits=1;
		return;
	}
};

Number _operatorAdd(Number &a,Number &b)
{
	Number c;
	int calcBits=max(a.bits,b.bits);
	for(int i=0;i<calcBits;i++)
	{
		c.n[i]+=a.n[i]+b.n[i];
		c.n[i+1]+=c.n[i]/NUM_PER_BIT;
		c.n[i]%=NUM_PER_BIT;
	}
	c.Settle();
	return c;
}

Number _operatorMulti(Number &a,Number &b)
{
	Number c;
	for(int i=0;i<a.bits;i++)
	{
		for(int j=0;j<b.bits;j++)
		{
			c.n[i+j]+=a.n[i]*b.n[j];
			c.n[i+j+1]+=c.n[i+j]/NUM_PER_BIT;
			c.n[i+j]%=NUM_PER_BIT;
			int k=i+j+1;
			while(c.n[k]>=NUM_PER_BIT)
			{
				c.n[k+1]+=c.n[k]/NUM_PER_BIT;
				c.n[k]%=NUM_PER_BIT;
				k++;
			}
		}
	}
	c.Settle();
	return c;
}

Number _operatorSub(Number &a,Number &b)
{
	Number c;
	for(int i=0;i<a.bits;i++)
	{
		c.n[i]+=a.n[i]-b.n[i];
		while(c.n[i]<0)
		{
			c.n[i]+=NUM_PER_BIT;
			c.n[i+1]--;
		}
	}
	c.Settle();
	return c;
}

int _operatorCompare(Number &a,Number &b)
{
	//a>b 1  a<b -1
	if(a.bits==b.bits)
	{
		for(int i=a.bits;i>=0;i--)
		{
			if(a.n[i]==b.n[i])continue;
			if(a.n[i]>b.n[i])
			{
				return 1;
			}
			if(a.n[i]<b.n[i])
			{
				return -1;
			}
		}
	}
	else
	{
		if(a.bits<b.bits)
		{
			return -1;
		}
		if(a.bits>b.bits)
		{
			return 1;
		}
	}

	return 0;
}
bool operator<(Number &a,Number &b)
{
	return _operatorCompare(a,b)==-1;
}
bool operator>(Number &a,Number &b)
{
	return _operatorCompare(a,b)==1;
}
bool operator==(Number &a,Number &b)
{
	return _operatorCompare(a,b)==0;
}
Number operator+(Number &a,Number &b)
{
	return _operatorAdd(a,b);
}
Number operator-(Number &a,Number &b)
{
	if(a<b)
	{
		Number tmp=_operatorSub(b,a);
		tmp.symbol=!tmp.symbol;
		return tmp;
	}
	else
	{
		return _operatorSub(a,b);
	}
}
Number operator*(Number &a,Number &b)
{
	return _operatorMulti(a,b);
}

string s1="",s2="";
int main()
{
	
	Number numa,numb;

	cin >>s1>>s2;
	numa.fromString(s1);
	numb.fromString(s2);
	cout <<(numa*numb).toString()<<endl;
	return 0;
}