第7章例题--2981--大整数加法

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

using namespace std;

const int maxn = 1000;

struct bign
{
       int len, s[maxn];  //s是逆序存储
       
       bign(){ memset(s, 0 , sizeof(s)); len = 1 ; } //构造函数
       
       bign(int num) { *this  = num ; } //初始化
       
       bign(const char* num) { *this = num ; }
        
       string str() const
       {
           int i;
		   string res = "";
           for( i = 0 ; i < len ; i++ ) 
               res = (char)( s[i] + '0' ) + res ;
           if (res == "") res = "0";
           return res;
       } 
        
       bign operator = (const char* num)
       {
            int i;
            len = strlen(num);
            for( i = 0 ; i < len ; i++ )
                s[i] = num[len-i-1] - '0' ;
            return *this; 
       } 
       
       bign operator = (int num)
       {
            char s[maxn];
            sprintf(s , "%d" , num);
            *this = s;
            return *this;
       } 
       
       bign operator + (const bign& b) const
       {
            bign c;
            c.len = 0;
            int i, g;
			for( i = 0 , g = 0 ; g || i < ( len > b.len ? 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;
       }
};

istream& operator >> (istream &in , bign& x)
{
	     string s;
         in >> s;
         x = s.c_str();
         return in;
}
ostream& operator << (ostream &out , const bign& x)
{
         out << x.str();
         return out;
}

int main()
{
	bign a,b;
	cin >> a;
	cin >> b;
	cout << (a + b) << endl;
	return 1;
}