c++大数模板

//支持正数的运算。两数相减也要为正数 
#include
#include
using namespace std;
const int maxn=10000;
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 = (const int num)  
    {  
        char s[maxn];  
        sprintf(s, "%d", num);  
        *this = s;  
        return *this;  
    }  
    bign operator = (const char *num)  
    {  
        for(int i = 0; num[i] == '0'; num++) ;  //去前导0  
        len = strlen(num);  
        for(int i = 0; i < len; i++) s[i] = num[len-i-1] - '0';  
        return *this;  
    }  
    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;  
    }  
    bign operator += (const bign &b)  
    {  
        *this = *this + b;  
        return *this;  
    }  
    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; i++)  
        {
            c.s[i+1] += c.s[i]/10;  
            c.s[i] %= 10;  
        }
        c.clean();
        return c;
    }
    bign operator *= (const bign &b)  
    {
        *this = *this * b;  
        return *this;  
    }
    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;  
    }  
    bign operator -= (const bign &b)  
    {  
        *this = *this - b;  
        return *this;  
    }  
    bign operator / (const bign &b)  
    {  
        bign c, f = 0;  
        for(int i = len-1; i >= 0; i--)  
        {  
            f = f*10;  
            f.s[0] = s[i];  
            while(f >= b)  
            {  
                f -= b;  
                c.s[i]++;  
            }  
        }  
        c.len = len;  
        c.clean();  
        return c;  
    }  
    bign operator /= (const bign &b)  
    {  
        *this  = *this / b;  
        return *this;  
    }  
    bign operator % (const bign &b)  
    {  
        bign r = *this / b;  
        r = *this - r*b;  
        return r;  
    }  
    bign operator %= (const bign &b)  
    {  
        *this = *this % b;  
        return *this;  
    }  
    bool operator < (const bign &b)  
    {  
        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)  
    {  
        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)  
    {  
        return !(*this > b) && !(*this < b);  
    }  
    bool operator != (const bign &b)  
    {  
        return !(*this == b);  
    }  
    bool operator <= (const bign &b)  
    {  
        return *this < b || *this == b;  
    }  
    bool operator >= (const bign &b)  
    {  
        return *this > b || *this == b;  
    }  
    string str() const  
    {  
        string res = "";  
        for(int i = 0; i < len; i++) res = char(s[i]+'0') + res;  
        return res;  
    }
};

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;
	cout<