func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long int mod = 1e9 + 7;   void solve() {     long long int a, s;     cin >> a >> s;     vector<long long int> b;     while (s) {       long long int x = a % 10;       long long int y = s % 10;       if (y >= x) {         b.push_back(y - x);       } else {         s /= 10;         y += 10 * (s % 10);         if (y > x && y <= 18 && y >= 10) {           b.push_back(y - x);         } else {           cout << -1 <<   n ;           return;         }       }       s /= 10;       a /= 10;     }     if (a) {       cout << -1 <<   n ;       return;     }     while (b.back() == 0) b.pop_back();     reverse((b).begin(), (b).end());     for (long long int x : b) cout << x;     cout <<   n ;   }   int32_t main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     long long int T = 1;     cin >> T;     for (long long int i = 1; i <= T; i++) {       solve();     }     return 0;   }   