Which part of this C code is missing or needs to be altered?
<p>For my assignment, I have to fill in missing parts of the C code below. 
However, I am not sure which parts are missing or which part I have to fill in.
I have a sample assembly code which this code will generate, but do not know which parts I have to change to get my expected result. I am just looking for clarification.</p>

<pre><code>typedef enum {MODE_A, MODE_B, MODE_C, MODE_D, MODE_E} mode_t;
long switch3 (long *p1, long *p2, mode_t action) {
  long result = 0;
  switch(action){
  case MODE_A:
  case MODE_B:
  case MODE_C:
  case MODE_D:
  case MODE_E:
  default;
  }
  return result;
}
</code></pre>

<p>Other points:</p>

<ul>
<li>There may be cases that should be written in the C
code with a fall-through</li>
<li>Code shows branching on an enumerated type value in a switch
statement. (Question: what exactly does this mean in simple terms? My professor provided a complex definition that I do not understand.)</li>
</ul>

<p><strong>Assembly code result example:</strong></p>

<pre><code># p1 in %rdi, p2 in %rsi, action in %edx
.L2:                         # MODE_E
      movl    $27, %eax
      ret
.L7:                         # MODE_A
      movl    (%rsi), %rax
      movq    (%rdi), %rdx
      movq     %rdx, (%rsi)
      ret
.L5:                         # MODE_B
      movq     (%rdi), %rax
      addq     (%rsi), %rax
      movq      %rax, (%rdi)
      ret
.L4:                         # MODE_C
      movq     $59, (%rdi)
      movq     (%rsi), %rax
      ret
.L3:                         # MODE_D
      movq     (%rsi), %rax
      movq      %rax, (%rdi)
      movl      $27, %eax
      ret
.L8:                         # default
      movl      $12, %eax
      ret
</code></pre>