BigInt by Jan vai

/**
*Author : Jan
*Problem Name : Big int for contest
*Algorithm :
*Complexity :
**/

#include <cstdio>
#include <string>
#include <cstring>
#include <algorithm>
#include<iostream>
using namespace std;

struct Bigint {
string a;
int sign;

Bigint() {}
Bigint( string b ) { (*this) = b; }
int size() { return a.size(); }
Bigint inverseSign() { sign *= -1; return (*this); }
Bigint normalize( int newSign ) {
sign = newSign;
for( int i = a.size() - 1; i > 0 && a[i] == '0'; i-- ) a.erase(a.begin() + i);
if( a.size() == 1 && a[0] == '0' ) sign = 1;
return (*this);
}
void operator = ( string b ) {
a = b[0] == '-' ? b.substr(1) : b;
reverse( a.begin(), a.end() );
this->normalize( b[0] == '-' ? -1 : 1 );
}
bool operator < ( const Bigint &b ) const {
if( a.size() != b.a.size() ) return a.size() < b.a.size();
for( int i = a.size() - 1; i >= 0; i-- ) if( a[i] != b.a[i] ) return a[i] < b.a[i];
return false;
}
Bigint operator + ( Bigint b ) {
if( sign != b.sign ) return (*this) - b.inverseSign();
Bigint c;
for( int i = 0, carry = 0; i < (int)a.size() || i < (int)b.size() || carry; i++ ) {
carry += (i < (int)a.size() ? a[i] - 48 : 0) + (i < (int)b.a.size() ? b.a[i] - 48 : 0);
c.a += (carry % 10 + 48);
carry /= 10;
}
return c.normalize(sign);
}
Bigint operator - ( Bigint b ) {
if( sign != b.sign ) return (*this) + b.inverseSign();
if( (*this) < b ) return (b - (*this)).inverseSign();
Bigint c;
for( int i = 0, borrow = 0; i < (int)a.size(); i++ ) {
borrow = a[i] - borrow - (i < b.size() ? b.a[i] : 48);
c.a += borrow >= 0 ? borrow + 48 : borrow + 58;
borrow = borrow >= 0 ? 0 : 1;
}
return c.normalize(sign);
}
Bigint operator * ( Bigint b ) {
Bigint c("0");
for( int i = 0, k = a[i]; i < (int)a.size(); i++, k = a[i] ) {
while(k-- - 48) c = c + b;
b.a.insert(b.a.begin(), '0');
}
return c.normalize(sign * b.sign);
}
Bigint operator / ( Bigint b ) {
if( b.size() == 1 && b.a[0] == '0' ) b.a[0] /= ( b.a[0] - 48 ) ;
Bigint c("0"), d;
for( int j = 0; j < (int)a.size(); j++ ) d.a += "0";
int dSign = sign * b.sign; b.sign = 1;
for( int i = a.size() - 1; i >= 0; i-- ) {
c.a.insert( c.a.begin(), '0');
c = c + a.substr( i, 1 );
while( !( c < b ) ) c = c - b, d.a[i]++;
}
return d.normalize(dSign);
}
Bigint operator % ( Bigint b ) {
if( b.size() == 1 && b.a[0] == '0' ) b.a[0] /= ( b.a[0] - 48 ) ;
Bigint c("0");
int cSign = sign * b.sign; b.sign = 1;
for( int i = a.size() - 1; i >= 0; i-- ) {
c.a.insert( c.a.begin(), '0');
c = c + a.substr( i, 1 );
while( !( c < b ) ) c = c - b;
}
return c.normalize(cSign);
}
void print() {
if( sign == -1 ) putchar('-');
for( int i = a.size() - 1; i >= 0; i-- ) putchar(a[i]);
}
};

int main() {

Bigint a, b, c;
string p,q;

cin>>p>>q;
a=p;
b=q;

c = a + b;

c.print();

putchar('\n');

c = a - b;
c.print();
putchar('\n');

c = a * b;
c.print();
putchar('\n');

c = a / b;
c.print();
putchar('\n');

c = a % b;
c.print();
putchar('\n');

return 0;
}