How does one fix "a is not defined" Reference Error?

Continuing the discussion from freeCodeCamp Challenge Guide: Adding a default option in Switch statements:

function switchOfStuff(val) {
  var answer = "";
  // Only change code below this line
  switch (answer) {case 'a': answer = 'apple';
                  break;
    case 'b': answer = 'bird';
                  break;
    case 'c': answer = 'cat';
                  break;
    default: answer ='stuff';}
  
  
  // Only change code above this line  
  return answer;  
}

// Change this value to test
switchOfStuff(a);

I meant to say this is lesson 184!
Here is the copy of a correct answer (posted on the above link):

Function switchOfStuff(val) {
var answer = "";
// Only change code below this line
switch (val){
case 'a':
answer = "apple";
break;
case 'b':
answer = "bird";
break;
case 'c':
answer = "cat";
break;
default:
answer = "stuff";
}

// Only change code above this line
return answer;
}

// Change this value to test
switchOfStuff(1);

I’m moving on, but I still was wondering what I did wrong in terms of formatting in my first post. Please let me know if you have a chance!

The challenges aren’t numbered. Those are your brownie points.

<code>
function switchOfStuff(val) {
  var answer = "";
  // Only change code below this line
  switch (val){
      case 'a':
      answer = ("apple");
      break;
      case 'b':
      answer = ("bird");
      break;
      case 'c':
      answer = ("cat");
      break;
      case 'd':
      answer = ("stuff");
      break;
      case 4:
      answer = ("stuff");
      break;
    default:
      answer = ("default");
      
  }
  
  
  // Only change code above this line  
  return answer;  
}

// Change this value to test
switchOfStuff(1);
</code>

I found that the number **4**
broke my code because it was surrounded by quotes. removed the quotes and tests pass