Sum BigNum

#include <bits/stdc++.h>
using namespace std;

int StringtoNum(char c) {
    return c - '0';
}

char NumtoString(int n) {
    return (char)(n + 48);
}

// lam 2 xau co do dai bang nhau
void ChuanHoa(string &a, string &b) {
    int l1 = a.length(), l2 = b.length();
    if(l1 >= l2)
        // chen vao dau cua b cac ky tu '0'
       b.insert(0, l1 - l2, '0');
    else
        // chen vao dau cua a cac ky tu '0'
       a.insert(0, l2-l1, '0');
}

string SUM(string a, string b) {
    string s = "";
    ChuanHoa(a,b);

    int tmp = 0;
    for(int i = a.length()-1; i >= 0; i--)
    {
        // tinh tong tung doi mot
        tmp = StringtoNum(a[i]) + StringtoNum(b[i]) + tmp;

        // gan phan don vi vao
       s.insert(0,1, NumtoString(tmp%10));

        // lay lai phan hang chuc
        tmp = tmp / 10;
    }

    // neu hang chuc > 0 thi them vao KQ
    if(tmp > 0)
        s.insert(0, 1, NumtoString(tmp));

    return s;
}

// nhan so co 1 chu so voi so co nhieu chu so, lam tuong tu nhu phep cong
string TichNho(char a, string b) {
    string s = "";
    int tmp = 0;

    for(int i = b.length()-1; i >= 0; i--)
    {
       tmp = StringtoNum(a) * StringtoNum(b[i]) + tmp;

       s.insert(0,1, NumtoString(tmp%10));

       tmp = tmp / 10;
    }

    if(tmp > 0)
        s.insert(0, 1, NumtoString(tmp));

    return s;
}

string TICH(string a, string b) {
    string s = "";
    int le = a.length();
    string s1[le];

     // nhan tung chu so cua a voi b sau do cong don vao
    for(int i = le-1; i >= 0; i--) {
        // nhan tung so cua a voi b
       s1[i] = TichNho(a[i], b);

       s1[i].insert(s1[i].length(), le-i-1, '0');

        // cong don theo cach cong so lon
       s = SUM(s, s1[i]);
    }

    return s;
}

string a, b;


int main() {
   int t; cin >> t;
   getline(cin, a);
   while(t--) {
        getline(cin, a);
        getline(cin, b);

        cout << "Tong: " << SUM(a, b) << '\n';

        cout << "Tich: " << TICH(a, b) << '\n';
   }

    return 0;
}