高精度大数的模板--c++代码

（后续如果复习的话，加注释）上代码：

#include <iostream>
#include<memory.h>
#include<string>
#include<cstdlib>
using namespace std;

#define MAXVALUE 9999

class BigNum{
private:
    int a[500];
    int len;
public:
    BigNum(){
        len=1;
        memset(a,0,sizeof(a));
    }
    BigNum(const int);
    BigNum(const char* );
    BigNum(const BigNum&);
    BigNum & operator=(const BigNum&);

    friend istream &operator>>(istream &,BigNum &);
    friend ostream &operator<<(ostream &,BigNum &);

    BigNum operator +(const BigNum &) const;
    BigNum operator -(const BigNum &) const;
    BigNum operator *(const BigNum &) const;
    BigNum operator /(const int &)const;

    BigNum operator^(const int &) const;
    int operator %(const int &) const;
    bool operator >(const BigNum &)const;
    bool operator >(const int &)const;

    void print();
};
BigNum::BigNum(const int b){
    int tmp,d=b;
    len=0;
    memset(a,sizeof(a));
    while(d>MAXVALUE){
        //tmp=d-d/(MAXVALUE+1)*(MAXVALUE+1);
        tmp=d%(MAXVALUE+1);
        d=d/(MAXVALUE+1);
        a[len++]=tmp;
    }
    a[len++]=d;
}
BigNum::BigNum(const char*s){
    len=0;
    memset(a,sizeof(a));
    int l=strlen(s);
    for(int i=l-1;i>=0;){
            int tmp=1;int sum=0;
        for(int j=0;j<4&&i>=0;j++,i--,tmp*=10){
            sum+=(s[i]-'0')*tmp;
        }
        a[len++]=sum;
    }
    while(a[len-1]==0&&len>1)
        len--;
}

BigNum::BigNum(const BigNum &T):len(T.len){
    memset(a,sizeof(a));
    for(int i=0;i<len;i++)
        a[i]=T.a[i];
}
BigNum & BigNum::operator=(const BigNum &n){
    len=n.len;
    memset(a,sizeof(a));
    for(int i=0;i<len;i++)
        a[i]=n.a[i];
    return *this;
}

istream &operator>>(istream& in,BigNum &b){
    string ch;
    in>>ch;//用cin代替in---测试好像没什么问题。
    int l=ch.size();
    int count=0;
    for(int i=l-1;i>=0;){
        int sum=0,t=1;
        for(int j=0;j<4&&i>=0;j++,t*=10)
            sum+=(ch[i]-'0')*t;
        b.a[count++]=sum;
    }
    b.len=count;
    return in;
}
ostream &operator <<(ostream &out,BigNum &b){
    out<<b.a[b.len-1];//将out替换成cout---也么有什么问题。奇怪
    for(int i=b.len-2;i>=0;i--){
        out.width(4);
        out.fill('0');
        out<<b.a[i];
    }
    return out;
}
BigNum BigNum::operator+(const BigNum &T) const{
    BigNum t(*this);
    int big=T.len>len?T.len:len;
    for(int i=0;i<big;i++){
        t.a[i]+=T.a[i];
        if(t.a[i]>MAXVALUE){
            t.a[i+1]++;
            t.a[i]-=MAXVALUE+1;
        }
    }
    if(t.a[big]!=0)
        t.len=big+1;
    else
        t.len=big;
    return t;
}

BigNum BigNum::operator-(const BigNum &T)const{
    BigNum t1,t2;
    bool flag;
    if(*this>T){
        t1=*this;
        t2=T;
        flag=false;
    }
    else{
        t1=T;
        t2=*this;
        flag=true;
    }
    int big=t1.len;
    for(int i=0;i<big;i++){
        if(t1.a[i]<t2.a[i]){
            int j=i+1;
            while(t1.a[j]==0)j++;
            t1.a[j--]--;
            while(j>i)t1.a[j--]+=MAXVALUE;
            t1.a[i]+=MAXVALUE+1-t2.a[i];
        }
        else
            t1.a[i]-=t2.a[i];
    }
    t1.len=big;
    while(t1.a[t1.len-1]==0&&t1.len>1){
        t1.len--;
    }
    if(flag)
        t1.a[t1.len-1]=0-t1.a[t1.len-1];
    return t1;
}

BigNum BigNum::operator*(const BigNum &T)const{
        BigNum res;
        int up;int i,j;
        for(i=0;i<len;i++){
            up=0;
            for(j=9;j<T.len;j++){
                int tmp=a[i]*T.a[j]+res.a[i+j]+up;
                if(tmp>MAXVALUE){
                    int tmp1=tmp%(MAXVALUE+1);
                    up=tmp/(MAXVALUE+1);
                    res.a[i+j]=tmp1;
                }
                else{
                    up=0;
                    res.a[i+j]=tmp;
                }
            }
            res.a[i+j]=up;
        }
        res.len=i+j;
        while(res.a[res.len-1]==0&&res.len>1)
            res.len--;
        return res;
}
BigNum BigNum::operator/(const int &b)const{
    BigNum res;
    int i,down=0;
    for(i=len-1;i>=0;i--){
        res.a[i]=(a[i]+down*(MAXVALUE+1))/b;
        down=a[i]+down*(MAXVALUE+1)-res.a[i]*b;
    }
    res.len=len;
    while(res.a[res.len-1]==0&&res.len>1)
        res.len--;
    return res;
}
int BigNum::operator%(const int &b)const{
    int i,d=0;
    for(i=len-1;i>=0;i--){
        //d=(d*(MAXVALUE+1)%b+a[i])%b;
        d=(d*(MAXVALUE+1)+a[i])%b;
    }
    return d;
}
BigNum BigNum::operator^(const int& n)const{
    BigNum t,ret(1);
    if(n<0)
        exit(-1);
    if(n==0)
        return 1;
    if(n==1)
        return *this;
    int m=n;
    t=*this;
    for(;m!=0;m>>=1){
        if(m&1)
            ret=ret*t;
        t=t*t;
    }
    return ret;
}

bool BigNum::operator>(const BigNum& T)const{
    if(len>T.len)
        return true;
    else if(len==T.len){
        int ln=len-1;
        while(a[ln]==T.a[ln]&&ln>=0)
            ln--;
        if(ln>=0&&a[ln]>T.a[ln])
            return true;
        else
            return false;
    }
    else
         return false;
}
bool BigNum::operator>(const int &t)const{
    BigNum b(t);
    return *this>b;
}
void BigNum::print(){
    int l=(*this).len;
    cout<<*this;
    cout<<"'s length ="<<l<<endl;
}

int main()
{
    BigNum T;
    BigNum T1("0909798798732");
    cin>>T;
    T.print();
    T1.print();
    int d=T%3;
    cout << "Hello world!" << d<<endl;
    return 0;
}