bign(高精度运算模板)

来自刘汝佳的书

/****************************************************/
#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <stack>
#include <map>
#include <queue>
#include <algorithm>
#define EPS 1E-8
using namespace std;
typedef long long LL;
/****************************************************/
 
 const int maxn = 200;
 struct bign{
 int len, s[maxn];
 
 bign() {
     memset(s, 0, sizeof(s));
     len = 1;
 }
 
 bign(int num) {
     *this = num;
 }
 
 bign(const char* num) {
     *this = num;
 }
 
 bign operator = (int num) {
     char s[maxn];
     sprintf(s, "%d", num);
     *this = s;
     return *this;
 }
 
 bign operator = (const char* num) {
     len = strlen(num);
     for(int i = 0; i < len; i++) s[i] = num[len-i-1] - '0';
     return *this;
 }
 
 string str() const {
     string res = "";
     for(int i = 0; i < len; i++) res = (char)(s[i] + '0') + res;
     if(res == "") res = "0";
     return res;
 }
 
 bign operator + (const bign& b) const{
     bign c;
     c.len = 0;
     for(int i = 0, g = 0; g || i < max(len, b.len); i++) {
       int x = g;
       if(i < len) x += s[i];
       if(i < b.len) x += b.s[i];
       c.s[c.len++] = x % 10;
       g = x / 10;
     }
     return c;
 }
 
 void clean() {
     while(len > 1 && !s[len-1]) len--;
 }
 
 bign operator * (const bign& b) {
     bign c; c.len = len + b.len;
     for(int i = 0; i < len; i++)
       for(int j = 0; j < b.len; j++)
         c.s[i+j] += s[i] * b.s[j];
     for(int i = 0; i < c.len-1; i++){
       c.s[i+1] += c.s[i] / 10;
       c.s[i] %= 10;
     }
     c.clean();
     return c;
 }
 
 bign operator - (const bign& b) {
     bign c; c.len = 0;
     for(int i = 0, g = 0; i < len; i++) {
       int x = s[i] - g;
       if(i < b.len) x -= b.s[i];
       if(x >= 0) g = 0;
       else {
         g = 1;
         x += 10;
       }
       c.s[c.len++] = x;
     }
     c.clean();
     return c;
 }
 
 bool operator < (const bign& b) const{
     if(len != b.len) return len < b.len;
     for(int 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) {
     return !(b > *this);
 }
 
 bool operator == (const bign& b) {
     return !(b < *this) && !(*this < b);
 }
 
 bign operator += (const bign& b) {
     *this = *this + b;
     return *this;
 }
 };