foo.cc: In member function ‘BigInt BigInt::operator+(const BigInt&) const’:
foo.cc:31:1: error: expected primary-expression before ‘|’ token
   31 | | j >= 0 |
      | ^
foo.cc:32:1: error: expected primary-expression before ‘|’ token
   32 | | carry != 0) {
      | ^
foo.cc: In function ‘int main()’:
foo.cc:65:21: error: no match for ‘operator*’ (operand types are ‘BigInt’ and ‘BigInt’)
   65 |         num1 = num1 * BigInt(x1);
      |                ~~~~ ^ ~~~~~~~~~~
      |                |      |
      |                BigInt BigInt
foo.cc:70:21: error: no match for ‘operator*’ (operand types are ‘BigInt’ and ‘BigInt’)
   70 |         num2 = num2 * BigInt(x2);
      |                ~~~~ ^ ~~~~~~~~~~
      |                |      |
      |                BigInt BigInt