fix help return and detail err

server.c

@@ -210,17 +210,21 @@ int parse_args(int argc,const char * argv[] , in_port_t * port){
         if (strcmp(opt,"-h") == 0 || strcmp(opt,"--help") == 0)
         {
             help(argv[0]);
-            return 2;
+            return 0;
         }
         else if(strcmp(opt,"-p") == 0 || strcmp(opt,"--port") == 0){
             if (pos < argc){
                 const char * value = argv[pos++];
                 *port = atoi(value);
                 if (port == 0){ // either not number or zero 
+                    fprintf(stderr,"argument is either not number or zero\n");
                     return 2;
                 }
             }
-            else return 2; //failed to find argument.
+            else{
+                fprintf(stderr,"need argument\n"); 
+                return 2; //failed to find argument.
+            }
         }
     }
     return 0;