BigInteger Program in C++

Once I was searching for BigInteger programs in C++, then I found this one. I really don't remember the source, as I copied it then.
But now as I am using this program for many problems, I thought of adding this one as it is really good.

If you use Java or python, you will never need this program.
















// The BigInteger Ripper

#include <vector>
#include <cstdlib>
#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
typedef long long LL;
// base and base_digits must be consistent
const int base = 1000000000;
const int base_digits = 9;

struct bigint {
    vector<int> a;
    int sign;

    bigint() :
        sign(1) {
    }

    bigint(long long v) {
        *this = v;
    }

    bigint(const string &s) {
        read(s);
    }

    void operator=(const bigint &v) {
        sign = v.sign;
        a = v.a;
    }

    void operator=(long long v) {
        sign = 1;
        if (v < 0)
            sign = -1, v = -v;
        for (; v > 0; v = v / base)
            a.push_back(v % base);
    }

    bigint operator+(const bigint &v) const {
        if (sign == v.sign) {
            bigint res = v;

            for (int i = 0, carry = 0; i < (int) max(a.size(), v.a.size()) || carry; ++i) {
                if (i == (int) res.a.size())
                    res.a.push_back(0);
                res.a[i] += carry + (i < (int) a.size() ? a[i] : 0);
                carry = res.a[i] >= base;
                if (carry)
                    res.a[i] -= base;
            }
            return res;
        }
        return *this - (-v);
    }

    bigint operator-(const bigint &v) const {
        if (sign == v.sign) {
            if (abs() >= v.abs()) {
                bigint res = *this;
                for (int i = 0, carry = 0; i < (int) v.a.size() || carry; ++i) {
                    res.a[i] -= carry + (i < (int) v.a.size() ? v.a[i] : 0);
                    carry = res.a[i] < 0;
                    if (carry)
                        res.a[i] += base;
                }
                res.trim();
                return res;
            }
            return -(v - *this);
        }
        return *this + (-v);
    }

    void operator*=(int v) {
        if (v < 0)
            sign = -sign, v = -v;
        for (int i = 0, carry = 0; i < (int) a.size() || carry; ++i) {
            if (i == (int) a.size())
                a.push_back(0);
            long long cur = a[i] * (long long) v + carry;
            carry = (int) (cur / base);
            a[i] = (int) (cur % base);
            //asm("divl %%ecx" : "=a"(carry), "=d"(a[i]) : "A"(cur), "c"(base));
        }
        trim();
    }

    bigint operator*(int v) const {
        bigint res = *this;
        res *= v;
        return res;
    }

    friend pair<bigint, bigint> divmod(const bigint &a1, const bigint &b1) {
        int norm = base / (b1.a.back() + 1);
        bigint a = a1.abs() * norm;
        bigint b = b1.abs() * norm;
        bigint q, r;
        q.a.resize(a.a.size());

        for (int i = a.a.size() - 1; i >= 0; i--) {
            r *= base;
            r += a.a[i];
            int s1 = r.a.size() <= b.a.size() ? 0 : r.a[b.a.size()];
            int s2 = r.a.size() <= b.a.size() - 1 ? 0 : r.a[b.a.size() - 1];
            int d = ((long long) base * s1 + s2) / b.a.back();
            r -= b * d;
            while (r < 0)
                r += b, --d;
            q.a[i] = d;
        }

        q.sign = a1.sign * b1.sign;
        r.sign = a1.sign;
        q.trim();
        r.trim();
        return make_pair(q, r / norm);
    }

    bigint operator/(const bigint &v) const {
        return divmod(*this, v).first;
    }

    bigint operator%(const bigint &v) const {
        return divmod(*this, v).second;
    }

    void operator/=(int v) {
        if (v < 0)
            sign = -sign, v = -v;
        for (int i = (int) a.size() - 1, rem = 0; i >= 0; --i) {
            long long cur = a[i] + rem * (long long) base;
            a[i] = (int) (cur / v);
            rem = (int) (cur % v);
        }
        trim();
    }

    bigint operator/(int v) const {
        bigint res = *this;
        res /= v;
        return res;
    }

    int operator%(int v) const {
        if (v < 0)
            v = -v;
        int m = 0;
        for (int i = a.size() - 1; i >= 0; --i)
            m = (a[i] + m * (long long) base) % v;
        return m * sign;
    }

    void operator+=(const bigint &v) {
        *this = *this + v;
    }
    void operator-=(const bigint &v) {
        *this = *this - v;
    }
    void operator*=(const bigint &v) {
        *this = *this * v;
    }
    void operator/=(const bigint &v) {
        *this = *this / v;
    }

    bool operator<(const bigint &v) const {
        if (sign != v.sign)
            return sign < v.sign;
        if (a.size() != v.a.size())
            return a.size() * sign < v.a.size() * v.sign;
        for (int i = a.size() - 1; i >= 0; i--)
            if (a[i] != v.a[i])
                return a[i] * sign < v.a[i] * sign;
        return false;
    }

    bool operator>(const bigint &v) const {
        return v < *this;
    }
    bool operator<=(const bigint &v) const {
        return !(v < *this);
    }
    bool operator>=(const bigint &v) const {
        return !(*this < v);
    }
    bool operator==(const bigint &v) const {
        return !(*this < v) && !(v < *this);
    }
    bool operator!=(const bigint &v) const {
        return *this < v || v < *this;
    }

    void trim() {
        while (!a.empty() && !a.back())
            a.pop_back();
        if (a.empty())
            sign = 1;
    }

    bool isZero() const {
        return a.empty() || (a.size() == 1 && !a[0]);
    }

    bigint operator-() const {
        bigint res = *this;
        res.sign = -sign;
        return res;
    }

    bigint abs() const {
        bigint res = *this;
        res.sign *= res.sign;
        return res;
    }

    long long longValue() const {
        long long res = 0;
        for (int i = a.size() - 1; i >= 0; i--)
            res = res * base + a[i];
        return res * sign;
    }

    friend bigint gcd(const bigint &a, const bigint &b) {
        return b.isZero() ? a : gcd(b, a % b);
    }
    friend bigint lcm(const bigint &a, const bigint &b) {
        return a / gcd(a, b) * b;
    }

    void read(const string &s) {
        sign = 1;
        a.clear();
        int pos = 0;
        while (pos < (int) s.size() && (s[pos] == '-' || s[pos] == '+')) {
            if (s[pos] == '-')
                sign = -sign;
            ++pos;
        }
        for (int i = s.size() - 1; i >= pos; i -= base_digits) {
            int x = 0;
            for (int j = max(pos, i - base_digits + 1); j <= i; j++)
                x = x * 10 + s[j] - '0';
            a.push_back(x);
        }
        trim();
    }
   
    int length(){
    int l=0,back=a.back();
    while(back){l++;back/=10;}
    l+=((a.size()-1)*base_digits);
    return l;
    }

    friend istream& operator>>(istream &stream, bigint &v) {
        string s;
        stream >> s;
        v.read(s);
        return stream;
    }

    friend ostream& operator<<(ostream &stream, const bigint &v) {
        if (v.sign == -1)
            stream << '-';
        stream << (v.a.empty() ? 0 : v.a.back());
        for (int i = (int) v.a.size() - 2; i >= 0; --i)
            stream << setw(base_digits) << setfill('0') << v.a[i];
        return stream;
    }

    static vector<int> convert_base(const vector<int> &a, int old_digits, int new_digits) {
        vector<long long> p(max(old_digits, new_digits) + 1);
        p[0] = 1;
        for (int i = 1; i < (int) p.size(); i++)
            p[i] = p[i - 1] * 10;
        vector<int> res;
        long long cur = 0;
        int cur_digits = 0;
        for (int i = 0; i < (int) a.size(); i++) {
            cur += a[i] * p[cur_digits];
            cur_digits += old_digits;
            while (cur_digits >= new_digits) {
                res.push_back(int(cur % p[new_digits]));
                cur /= p[new_digits];
                cur_digits -= new_digits;
            }
        }
        res.push_back((int) cur);
        while (!res.empty() && !res.back())
            res.pop_back();
        return res;
    }

    typedef vector<long long> vll;

    static vll karatsubaMultiply(const vll &a, const vll &b) {
        int n = a.size();
        vll res(n + n);
        if (n <= 32) {
            for (int i = 0; i < n; i++)
                for (int j = 0; j < n; j++)
                    res[i + j] += a[i] * b[j];
            return res;
        }

        int k = n >> 1;
        vll a1(a.begin(), a.begin() + k);
        vll a2(a.begin() + k, a.end());
        vll b1(b.begin(), b.begin() + k);
        vll b2(b.begin() + k, b.end());

        vll a1b1 = karatsubaMultiply(a1, b1);
        vll a2b2 = karatsubaMultiply(a2, b2);

        for (int i = 0; i < k; i++)
            a2[i] += a1[i];
        for (int i = 0; i < k; i++)
            b2[i] += b1[i];

        vll r = karatsubaMultiply(a2, b2);
        for (int i = 0; i < (int) a1b1.size(); i++)
            r[i] -= a1b1[i];
        for (int i = 0; i < (int) a2b2.size(); i++)
            r[i] -= a2b2[i];

        for (int i = 0; i < (int) r.size(); i++)
            res[i + k] += r[i];
        for (int i = 0; i < (int) a1b1.size(); i++)
            res[i] += a1b1[i];
        for (int i = 0; i < (int) a2b2.size(); i++)
            res[i + n] += a2b2[i];
        return res;
    }

    bigint operator*(const bigint &v) const {
        vector<int> a6 = convert_base(this->a, base_digits, 6);
        vector<int> b6 = convert_base(v.a, base_digits, 6);
        vll a(a6.begin(), a6.end());
        vll b(b6.begin(), b6.end());
        while (a.size() < b.size())
            a.push_back(0);
        while (b.size() < a.size())
            b.push_back(0);
        while (a.size() & (a.size() - 1))
            a.push_back(0), b.push_back(0);
        vll c = karatsubaMultiply(a, b);
        bigint res;
        res.sign = sign * v.sign;
        for (int i = 0, carry = 0; i < (int) c.size(); i++) {
            long long cur = c[i] + carry;
            res.a.push_back((int) (cur % 1000000));
            carry = (int) (cur / 1000000);
        }
        res.a = convert_base(res.a, 6, base_digits);
        res.trim();
        return res;
    }
};


void recursive_fraction(bigint a,bigint b)
{
  bigint n,i;
  if(a>b)
  {
    n=a/b;
    for(i=1;i<=n;i+=1)
    {
       cout<<"1 ";
    }
    a=(a-b*n);
  }
  while(a!=0)
  {
    n=b/a;
    if(b%a!=0) n=n+1;
    cout<<n<<" ";
    a=n*a-b;
    b=n*b;
  }
}
int main()
{
 while(true)
 {
      bigint num;
      cin>>num;
      if(num == -1)break;
      bigint nine = 9;
      bigint ans = num/nine;
      bigint zero = 0;
      if(num%nine != zero)
             ans = ans + 1;
      cout<<ans<<endl;
 }
  return 0;
}


PS: (My implementation of Biginteger add, multiply and subtraction, just coded it once in the beginning)

// My Implementation

#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
typedef long long int int64;
using namespace std;
char op1[100001],op2[100001],res[200003];

char * convert(int64 a,char * num)
{
     int len = int(log10(double(a)));
     num[len+1] = '\0';
     while(a>0)
     {
      num[len--] = a%10 + '0';
      a = a/10;        
     }
     return num;
}

char * convert(char * a,char * num)
{
     strcpy(num,a);
     return num;
}

char * reverse(char * num)
{
 char x[200003];int lo = 0;
 int len = strlen(num);
 while(num[len-1]=='0' && len>=1)
                       len--;

 if(len==0)
           {num[0]='0';num[1]='\0';return num;}

 for(int xx = len-1;xx>=0;xx--)
 {
         x[lo++] = num[xx];
 }  
 x[lo]='\0';
 strcpy(num,x);
 return num;
}

char * add(char * a, char * b, char * num)
{
     int len1 = strlen(a)-1;
     int len2 = strlen(b)-1;
     int carry = 0;
     int x = 0;
     while(len1>=0 && len2>=0)
     {
      int temp = a[len1--]-'0'+ b[len2--]-'0' + carry;            
      num[x++] = temp%10 + '0';
      carry = temp/10;
     }   
     while(len1>=0)
     {
      int temp = a[len1--]-'0'+ carry;            
      num[x++] = temp%10 + '0';
      carry = temp/10;
     }
     while(len2>=0)
     {
      int temp = b[len2--]-'0'+ carry;            
      num[x++] = temp%10 + '0';
      carry = temp/10;
     }
     if(carry>0)
                num[x++] = carry+'0';
     num[x] = '\0';   
     return reverse(num);
}

char * sub(char * a, char * b, char * num)
{
     int len1 = strlen(a)-1;
     int len2 = strlen(b)-1;
     int carry = 0;
     int x = 0;int togl = 0;
     while(len2>=0)
     {
      int temp;
      if(a[len1]>=b[len2])
      {
       temp = a[len1] - b[len2];
       num[x++] = temp + '0';                   
       len1--,len2--;
      }
      else
      {
       int flag;togl = 1;
       while(a[len1]<=b[len2])
       {
        if(togl==1){num[x++] = a[len1] - b[len2]+10 +'0';togl=0;}
        else {num[x++] = a[len1] - b[len2]+9 +'0';}
        len1--,len2--;            
        if(len2<0)
                  {flag=1;break;} 
       }  
       while(a[len1]=='0'){num[x++]='9';len1--;}
       num[x++] =    a[len1] - (flag==1?'0':b[len2]) - 1 +'0';
       len2--,len1--;
      }            
     }
     while(len1>=0)
                   num[x++]=a[len1--];
     num[x]= '\0';

     return reverse(num);
}


char * mult(char * a, char * b, char * num)
{
     int len1 = strlen(a)-1;
     int len2 = strlen(b)-1;
     int x=0,carry=0,ll=0,mm=0,prevll=-1;
     for(int i=len1;i>=0;i--)
     {
      int mul1 = a[i]-'0';
      for(int j=len2;j>=0;j--)      
             {
                int mul2 = b[j]-'0';          
                int temp = mul1*mul2 + carry + (mm<=prevll?num[mm]-'0':0);
                num[mm++] = temp%10 +'0';
                carry = temp/10;                                    
             }
             if(carry>0)
                        {num[mm++]=carry+'0';
                         carry = 0;}
             prevll = mm-1;
             ll++;
             if(i==0){num[mm]='\0';break;}
             mm = ll;
     }
     return reverse(num);
}



int main()
{
 char a[100001], b[100001];
 while(cin>>a>>b)
 {
  //cout<<add(convert(a,op1),convert(b,op2),res)<<endl;
  cout<<sub(convert(a,op1),convert(b,op2),res)<<endl;
  //cout<<mult(convert(a,op1),convert(b,op2),res)<<endl; 
 
 }
return 0;
}