BigInt Multiplication.cpp

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main(void)
{
    string s, t;
    while(cin >> s)
    {
        cin >> t;
        vector<int> v1, v2;
        for (int i = 0; i < (int)s.length(); i++)
            v1.resize(v1.size() + 1, s[i] - '0');
        for (int i = 0; i < (int)t.length(); i++)
            v2.resize(v2.size() + 1, t[i] - '0');
        reverse(v1.begin(), v1.end()); reverse(v2.begin(), v2.end());
        if (v1.front() != 0 && v2.front() != 0)
        {
            vector<int> v3(v1.size() + v2.size(), 0);
            for (int i = 0; i < (int)v1.size(); i++)
            {
                for (int j = 0; j < (int)v2.size(); j++)
                    v3[i + j] += v1[i] * v2[j];
            }
            for (int i = 0; i < (int)v3.size() - 1; i++)
            {
                v3[i + 1] += (v3[i] / 10);
                v3[i] %= 10;
            }
            if (v3.back() == 0)
                v3.erase(v3.end() - 1);
            reverse(v3.begin(), v3.end());
            for (int i = 0; i < (int)v3.size(); i++)
                cout << v3[i];
        }
        else cout << 0;
        cout << endl;
    }
    return 0;
}