高精度运算类bign

#ifndef BIGN_H_INCLUDED#define BIGN_H_INCLUDED#include <cstring>#include <iostream>#include <string>using namespace std;#define MAX_N 1000 //最大位数//大数struct bign {    char s[MAX_N];    int len;    bign() {        memset(s, 0, sizeof(s));        len = 1;    }    bign(int num) {        *this = num;    }    bign(const char *num) {        *this = num;    }    bign operator = (const char *num) {        len = strlen(num);        for(int i=0; i<len; i++) {            s[i] = num[len-1-i] - '0';        }        return *this;    }    bign operator = (int num) {        char s[MAX_N];        sprintf(s, "%d", num);        *this = s;        return *this;    }    bign operator + (const bign &b) const    {        bign c;        int m = len > b.len ? len : b.len;        int i, g, sum;        for(i=0, g=0; g || i< m; i++) {            sum = g;            if(i < len) sum += s[i];            if(i < b.len) sum += b.s[i];            c.s[i] = sum%10;            g = sum / 10;        }        c.len = i;        return c;    }    bign operator += (const bign &b)    {        *this = *this + b;        return *this;    }    bool operator < (const bign &b) const    {        if(b.len != len) return len < b.len;        int i;        for(i=len-1; i>=0; i--) {            if(s[i] != b.s[i]) return s[i] < b.s[i];        }        return false;    }    bool operator > (const bign &b) const { return b < *this;}    bool operator <= (const bign &b) const {return !(*this > b);}    bool operator >= (const bign &b) const {return !(*this < b);}    bool operator != (const bign &b) const {return (*this < b) || (*this > b);}    bool operator == (const bign &b) const {return !(*this < b) && !(*this > b);}};ostream& operator << (ostream& outstream, const bign& b){    for(int i=b.len-1; i>=0; i--) {        outstream << (int)b.s[i] << "";    }    return outstream;}istream& operator >> (istream& instream, bign& b){    string s;    instream >> s;    b = s.c_str();    return instream;}#endif // BIGN_H_INCLUDED