answer.code: In function ‘void add(int)’:
answer.code:110:5: error: ‘balance’ was not declared in this scope
  110 |     balance();
      |     ^~~~~~~
answer.code: In function ‘void del(int)’:
answer.code:154:5: error: ‘balance’ was not declared in this scope
  154 |     balance();
      |     ^~~~~~~