#include <string>
#include <vector>
#include <iostream>
#include <stdio.h>
using namespace std;
void product(string a, string b) {
vector<int> result(a.size() + b.size(), 0);
for( int i = a.size() - 1; i >= 0; i-- ){
    for( int j = b.size() - 1; j >= 0; j-- ){
        result[ i + j + 1 ] += ( b[ j ] - '0') * ( a[ i ] - '0' ); //single array to store intermediate values
    }
}
for( int i = a.size() + b.size(); i >= 0; i-- ){
    if( result[ i ] >= 10 ){
        result[ i - 1 ] +=result[ i ] / 10;result[ i ] %= 10;
    }
}
cout << a << " * " << b << " = ";
for( int i = 0; i < a.size() + b.size(); i++ ){
cout << result[ i ];
}
cout << endl;
}
int main( void ){
string str1, str2 ;
str1 = "99999999999999999999";str2 = "9985995948565498566";
product( str1, str2 );
}
return 0;