Balanced Brackets (CTCI)

Problem: Balanced Brackets

bool is_balanced(string expression) {
  stack<char>brackets;
  for(int i=0;i<expression.length();i++)
  {
      if(expression[i]=='(' || expression[i]=='{' || expression[i]=='[')
          brackets.push(expression[i]);
      else if(!brackets.empty())
      {
        if(expression[i]==')' && brackets.top()=='(') 
            brackets.pop();
         else if(expression[i]=='}' && brackets.top()=='{') 
            brackets.pop();
        else if(expression[i]==']' && brackets.top()=='[') 
            brackets.pop();
      }
      else return false;
  }
  if(brackets.empty()) return true;
  return false;
}