高精度模板

#ifndef _CLASS_BIGINTEGER_
#define _CLASS_BIGINTEGER_
#include<string>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
using namespace std;
typedef long long qword;
struct Int128
{
        static const qword maxval=100000000000000000LLU;
        qword first,second;
        Int128(qword x,qword y):first(x),second(y){};
        Int128(){};
        inline void operator += (Int128& pp)
        {
                first+=pp.first;
                second+=pp.second;
                if (second>=maxval)
                {
                        first++;
                        second-=maxval;
                }
        }
        inline void operator -=(Int128& pp)
        {
                first-=pp.first;
                second-=pp.second;
                if (second<0)
                {
                        second+=maxval;
                        first--;
                }
        }
};
class BigInteger
{
        public:
        static const int maxlen=10;
        static const int maxval=10000;
        private:
                int numb[maxlen];
                int len;
                bool sign;
                void Add(BigInteger &num);
                void Substract(BigInteger &num);
                void Multiply(const BigInteger &num);
                void Divide(const BigInteger &num);
                int AbsCompare(const BigInteger &num);
                int Compare(const BigInteger &num);
        public:
                BigInteger();
                BigInteger(long long x);
                BigInteger(string str);
                string ToString()const;
                void operator =(const BigInteger &num);
                void operator +=(const BigInteger num);
                void operator -=(const BigInteger num);
                void operator *=(const BigInteger num);
                void operator /=(const BigInteger num);
                bool operator <(const BigInteger &num);
                bool operator <=(const BigInteger &num);
                bool operator >(const BigInteger &num);
                bool operator >=(const BigInteger &num);
                friend ostream& operator << (ostream& out,const BigInteger& num);
                friend istream& operator >> (istream& in,BigInteger& num);
                friend BigInteger operator +(BigInteger num1,BigInteger num2);
                friend BigInteger operator -(BigInteger num1,BigInteger num2);
                friend BigInteger operator *(BigInteger num1,BigInteger num2);
};
#endif


BigInteger::BigInteger()
{
        memset(numb,0,sizeof(numb));
}
BigInteger::BigInteger(long long x)
{
        char s[20];
        sprintf(s,"%lld",x);
        string str=s;
        *this=BigInteger(str);
}
BigInteger::BigInteger(string str)
{
        memset(numb,0,sizeof(numb));
        sign=false;
        if (str[0]=='-')
        {
                sign=true;
                str=str.substr(1,str.length()-1);
        }
        for (int i=0;i<(int)str.length();i++)
        {
                if (!isdigit(str[i]))throw "invalid number!";
                numb[(str.length()-i-1)/4]=numb[(str.length()-i-1)/4]*10+str[i]-'0';
        }
        len=(int)(str.length()-1)/4+1;
        while (len && !numb[len-1])len--;
}
void BigInteger::Add(BigInteger &num)
{
        if (this->sign!=num.sign)
        {
                num.sign^=1;
                Substract(num);
                num.sign^=1;
        }else
        {
                len=max(len,num.len);
                for (int i=0;i<len;i++)
                        numb[i]+=num.numb[i];
                for (int i=0;i<len;i++)
                {
                        numb[i+1]+=numb[i]/maxval;
                        numb[i]%=maxval;
                }
                while (numb[len])
                {
                        numb[len+1]+=numb[len]/maxval;
                        numb[len]%=maxval;
                        if (len++==maxlen)throw "Out of range!";
                }
        }
}
void BigInteger::Substract(BigInteger &num)
{
        if (this->sign!=num.sign)
        {
                num.sign^=1;
                Add(num);
                num.sign^=1;
        }else
        {
                for (int i=0;i<len;i++)
                        numb[i]-=num.numb[i];
                for (int i=0;i<len;i++)
                {
                        if (numb[i]<0)
                        {
                                numb[i]+=maxval;
                                numb[i+1]--;
                        }
                }
                if (numb[len]<0)throw "Substract Error!";
                while (len && !numb[len-1])len--;
        }
}
int BigInteger::AbsCompare(const BigInteger &num)
{
        if (this->len!=num.len)
                return this->len<num.len?-1:1;
        for (int i=this->len-1;i>=0;i--)
        {
                if (this->numb[i]!=num.numb[i])
                        return this->numb[i]<num.numb[i]?-1:1;
        }
        return 0;
}
int BigInteger::Compare(const BigInteger &num)
{
        if (this->sign!=num.sign)
                return this->sign>num.len?-1:1;
        return AbsCompare(num);
}
string BigInteger::ToString()const
{
        string res;
        if (len || numb[0]!=0)res=sign?"-":"";
        char cstr[5];
        sprintf(cstr,"%d",numb[len-1]);
        res+=cstr;
        for (int i=len-2;i>=0;i--)
        {
                sprintf(cstr,"%04d",numb[i]);
                res+=cstr;
        }
        return res;
}
void BigInteger::operator =(const BigInteger &num)
{
        memcpy(this,&num,sizeof(num));
}
//void BigInteger::operator +=(BigInteger num){}
//void BigInteger::operator -=(BigInteger num){}
//void BigInteger::operator *=(BigInteger num){}
//void BigInteger::operator /=(BigInteger num){}
bool BigInteger::operator <(const BigInteger& num)
{
        return this->Compare(num)<0;
}
bool BigInteger::operator <=(const BigInteger& num)
{
        return this->Compare(num)<=0;
}
bool BigInteger::operator >(const BigInteger& num)
{
        return this->Compare(num)>0;
}
bool BigInteger::operator >=(const BigInteger& num)
{
        return this->Compare(num)>0;
}
ostream& operator << (ostream& out,const BigInteger& num)
{
        string str;
        str=num.ToString();
        out<<str;
        return out;
}
istream& operator >> (istream& in,BigInteger& num)
{
        string str;
        in>>str;
        num=BigInteger(str);
        return in;
}
BigInteger operator + (BigInteger num1,BigInteger num2)
{
        if (num1.AbsCompare(num2)>=0)
        {
                num1.Add(num2);
                return num1;
        }else
        {
                num2.Add(num1);
                return num2;
        }
}
BigInteger operator - (BigInteger num1,BigInteger num2)
{
        if (num1.AbsCompare(num2)>=0)
        {
                num1.Substract(num2);
                return num1;
        }else
        {
                num2.Substract(num1);
                num2.sign^=1;
                return num2;
        }
}
BigInteger operator * (BigInteger num1,BigInteger num2)
{
        BigInteger ret;
        ret.sign=num1.sign^num2.sign;
        ret.len=num1.len+num2.len;
        for (int i=0;i<num1.len;i++)
                for (int j=0;j<num2.len;j++)
                {
                        ret.numb[i+j]+=num1.numb[i]*num2.numb[j];
                        ret.numb[i+j+1]+=ret.numb[i+j]/BigInteger::maxval;
                        ret.numb[i+j]%=BigInteger::maxval;
                }
        for (int i=0;i<ret.len;i++)
        {
                ret.numb[i+1]+=ret.numb[i]/BigInteger::maxval;
                ret.numb[i]%=BigInteger::maxval;
        }
        while (ret.numb[ret.len])
        {
                ret.numb[ret.len+1]=ret.numb[ret.len]/BigInteger::maxval;
                ret.numb[ret.len]%=BigInteger::maxval;
                ret.len++;
        }
        while (ret.len && !ret.numb[ret.len-1])ret.len--;
        return ret;
}
int main()
{
        freopen("input.txt","r",stdin);
        BigInteger a,b,c;;
        cin>>a>>b;
        c=a*b;
        cout<<c<<endl;
}