第五章Biginteger部分实现

#include <cstdio>
#include <iostream>
#include <vector>

using namespace std;

struct BigInteger
{
    static const int BASE=100000000;
    static const int WIDTH=8;

    vector<int> s;

    BigInteger(long long int num=0){ *this=num; }

    BigInteger operator=(long long num)
    {
        s.clear();

        do
        {
            s.push_back(num%BASE);
            num/=BASE;

        }while(num>0);

        return *this;
    }

    BigInteger operator=(const string& num)
    {
        s.clear();

        for(int end=num.length()-1;;)
        {
            int x,start=end-WIDTH+1;

            if(start>=0)
            {
                sscanf(num.substr(start,WIDTH).c_str(),"%d",&x);
                s.push_back(x);
                end=start-1;
            }
            else if(end>=0)
            {
                sscanf(num.substr(0,end+1).c_str(),"%d",&x);
                s.push_back(x);
                break;
            }
            else
                break;
        }

        return *this;
    }

    BigInteger operator+(const BigInteger& b)
    {
        BigInteger c;
        c.s.clear();                 //必须先clear为空不然会有一个默认的0值在c.s 中

        int c1=0;

        for(unsigned int i=0;;i++)
        {
            if(i<s.size() && i<b.s.size())
            {
                int sum=s[i]+b.s[i]+c1;
                c1=sum/BASE;
                sum%=BASE;
                c.s.push_back(sum);
            }
            else if(i<s.size() && i>=b.s.size())
            {
                int sum=s[i]+c1;
                c1=sum/BASE;
                sum%=BASE;
                c.s.push_back(sum);
            }
            else if(i>=s.size() && i<b.s.size())
            {
                int sum=b.s[i]+c1;
                c1=sum/BASE;
                sum%=BASE;
                c.s.push_back(sum);
            }
            else if(i>=s.size() && i>=b.s.size())
            {
                if(c1==1)
                    c.s.push_back(c1);
                else
                    break;
            }
                
        }

        return c;
            
    }

    bool operator<(const BigInteger& b)
    {
        if(s.size()!=b.s.size()) return s.size()<b.s.size();

        for(unsigned int i=s.size()-1;i>=0;i--)
            if(s[i]!=b.s[i])
                return s[i]<b.s[i];

        return false;
    }

    friend ostream& operator<<(ostream& out,const BigInteger& x);
    friend istream& operator>>(istream& in,const BigInteger& x);
};

ostream& operator<<(ostream& out,const BigInteger& x)
{


    for(int i=x.s.size()-1;i>=0;i--)
    {
        if(x.s[i]==0)
        {
            for(int j=1;j<=x.WIDTH;j++)
                out<<0;
        }
        else
            out<<x.s[i];
    }

         //cout<<x.s.size()<<endl;
    return out;
}

istream& operator>>(istream& in,BigInteger& x)
{
    string s;
    if(!(in>>s)) return in;

    x=s;
    return in;
}

int main()
{
    BigInteger bi1;
    BigInteger bi2;

    cin>>bi1;
    cin>>bi2;


    if(bi1<bi2)
    {
        cout<<bi1<<endl;
        cout<<bi2<<endl;
    }
    else
    {
        cout<<bi2<<endl;
        cout<<bi1<<endl;
    }

    cout<<bi2+bi1<<endl;
    return 0;

}