大整数类（模板）

/*支持加减乘除、取模、赋值、输入输出*/
const int MAX_SIZE = 5000 + 10;  //最大位数

struct BigInteger
{
    int len, s[MAX_SIZE];
    BigInteger()
    {
        memset(s, 0, sizeof(s));
        len = 1;
    }
    BigInteger(int num) { *this = num; }
    BigInteger(const char *num) { *this = num; }
    void clean() { while (len > 1 && !s[len - 1])len--; }
    BigInteger operator = (const int num)
    {
        char s[MAX_SIZE];
        sprintf(s, "%d", num);
        *this = s;
        return *this;
    }
    BigInteger operator = (const char *num)
    {
        len = strlen(num);
        for (int i = 0; i < len; i++)s[i] = num[len - i - 1] - '0';
        return *this;
    }
    BigInteger operator + (const BigInteger& b)
    {
        BigInteger c;
        c.len = 0;
        for (int i = 0, g = 0; g || i < max(len, b.len); i++)
        {
            int x = g;
            if (i < b.len)x += b.s[i];
            if (i < len)x += s[i];
            c.s[c.len++] = x % 10;
            g = x / 10;
        }
        return c;
    }
    BigInteger operator - (const BigInteger& b)
    {
        BigInteger 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;
    }
    BigInteger operator * (const BigInteger& b)
    {
        BigInteger 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;
    }
    BigInteger operator * (const int& b)
    {
        BigInteger c;
        c.len = 0;
        for (int i = 0, g = 0; g || i < len; i++)
        {
            int x;
            if (i < len)x = s[i] * b + g;
            else x = g;
            c.s[c.len++] = x % 10;
            g = x / 10;
        }
        return c;
    }
    BigInteger operator / (const BigInteger& b)
    {
        BigInteger c, f = 0;
        for (int i = len - 1; i >= 0; i--)
        {
            f = f * 10;
            f.s[0] = s[i];
            while (f >= b)
            {
                f = f - b;
                c.s[i]++;
            }
        }
        c.len = len;
        c.clean();
        return c;
    }
    BigInteger operator / (const int& b)
    {
        BigInteger c, d = *this;
        c.len = len;
        for (int i = len - 1, g = 0; i >= 0; i--)
        {
            d.s[i] += g * 10;
            c.s[i] = d.s[i] / b;
            g = d.s[i] % b;
        }
        c.clean();
        return c;
    }
    BigInteger operator % (const BigInteger& b)
    {
        BigInteger c = *this / b;
        c = *this - c * b;
        return c;
    }
    BigInteger operator += (const BigInteger& b)
    {
        *this = *this + b; return *this;
    }
    BigInteger operator -= (const BigInteger& b)
    {
        *this = *this - b; return *this;
    }
    BigInteger operator *= (const BigInteger& b)
    {
        *this = *this*b; return *this;
    }
    BigInteger operator /= (const BigInteger& b)
    {
        *this = *this / b; return *this;
    }
    BigInteger operator *= (const int& b)
    {
        *this = *this*b; return *this;
    }
    BigInteger operator /= (const int& b)
    {
        *this = *this / b; return *this;
    }
    BigInteger operator %= (const BigInteger& b)
    {
        *this = *this%b; return *this;
    }
    bool operator < (const BigInteger& b)
    {
        if (b.len != 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 0;
    }
    bool operator > (const BigInteger& b)
    {
        if (b.len != 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 0;
    }
    bool operator == (const BigInteger& b)
    {
        return !(*this > b) && !(*this < b);
    }
    bool operator <= (const BigInteger& b)
    {
        return !(*this > b);
    }
    bool operator >= (const BigInteger& b)
    {
        return !(*this < b);
    }
    bool operator != (const BigInteger& b)
    {
        return !(*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, BigInteger &x)
{
    string s;
    in >> s;
    x = s.c_str();
    return in;
}
ostream& operator << (ostream&out, BigInteger x)
{
    out << x.str();
    return out;
}