func_code_string: #include <bits/stdc++.h>   using namespace std;   int toint(char a) { return (a -  0 ); }   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     int tst;     cin >> tst;     while (tst--) {       string a, s;       cin >> a >> s;       long long int num = stoll(a);       long long int sum = stoll(s);       if (s.length() < a.length()) {         cout <<  -1 n ;       } else if (a.length() == s.length()) {         bool no = false;         for (int i = s.length() - 1; i >= 0; i--) {           if ((toint(s[i]) - toint(a[i])) < 0) {             cout <<  -1 n ;             no = true;             break;           }         }         if (!no) {           cout << stoll(s) - stoll(a) <<   n ;         }       } else if (a.length() < s.length()) {         int lastdigit;         int lastsub;         string ans;         bool no = 0;         int strlen = s.length();         while (strlen > 0) {           lastsub = num % 10;           if (sum % 10 - num % 10 < 0) {             lastdigit = (sum % 10) + ((sum % 100) - (sum % 10));             sum /= 100;             num /= 10;             strlen -= 2;           } else {             lastdigit = sum % 10;             sum /= 10;             num /= 10;             strlen--;           }           if (lastdigit - lastsub >= 0 && lastdigit - lastsub <= 9) {             if (strlen != 0) {               ans = to_string(lastdigit - lastsub) + ans;             } else {               if (lastdigit - lastsub != 0) {                 ans = to_string(lastdigit - lastsub) + ans;               }             }           } else {             cout <<  -1 n ;             no = true;             break;           }         }         if (!no) {           cout << ans <<   n ;         }       }     }     return 0;   }   