else
   {
     i = 1;
-    while (plci->internal_command_queue[i] != 0)
+    while (plci->internal_command_queue[i] != NULL)
       i++;
     plci->internal_command_queue[i] = command_function;
   }
 
   plci->internal_command = 0;
   plci->internal_command_queue[0] = NULL;
-  while (plci->internal_command_queue[1] != 0)
+  while (plci->internal_command_queue[1] != NULL)
   {
     for (i = 0; i < MAX_INTERNAL_COMMAND_LEVELS - 1; i++)
       plci->internal_command_queue[i] = plci->internal_command_queue[i+1];
         dbug(1,dprintf("AdvSigPlci=0x%x",a->AdvSignalPLCI));
         return 0x2001; /* codec in use by another application */
       }
-      if(plci!=0)
+      if(plci!=NULL)
       {
         a->AdvSignalPLCI = plci;
         plci->tel=ADV_VOICE;
         }
                                                /* indicate D-ch connect if  */
       }                                        /* codec is connected OK     */
-      if(plci!=0)
+      if(plci!=NULL)
       {
         a->AdvSignalPLCI = plci;
         plci->tel=ADV_VOICE;
   {
     if(hook_listen) return 0x300B;               /* Facility not supported */
                                                  /* no hook with SCOM      */
-    if(plci!=0) plci->tel = CODEC;
+    if(plci!=NULL) plci->tel = CODEC;
     dbug(1,dprintf("S/SCOM codec"));
     /* first time we use the scom-s codec we must shut down the internal   */
     /* handset application of the card. This can be done by an assign with */
   int max_ch = ARRAY_SIZE(a->ch_flow_control);
   int i, one_requested = 0;
 
-  if ((!plci) || (!plci->Id) || ((a = plci->adapter) == 0)) {
+  if ((!plci) || (!plci->Id) || ((a = plci->adapter) == NULL)) {
     return;
   }