Weather update client in Objective-C

//
// Weather update client
// Connects SUB socket to tcp://localhost:5556
// Collects weather updates and finds avg temp in zipcode
//
#import "ZMQObjC.h"

int
main(int argc, const char *argv[])
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
ZMQContext *ctx = [[[ZMQContext alloc] initWithIOThreads:1U] autorelease];

// Socket to talk to server
ZMQSocket *subscriber = [ctx socketWithType:ZMQ_SUB];
if (![subscriber connectToEndpoint:@"tcp://localhost:5556"]) {
/* ZMQSocket will already have logged the error. */
return EXIT_FAILURE;
}

/* Subscribe to zipcode (defaults to NYC, 10001). */
const char *kNYCZipCode = "10001";
const char *filter = (argc > 1)? argv[1] : kNYCZipCode;
NSData *filterData = [NSData dataWithBytes:filter length:strlen(filter)];
[subscriber setData:filterData forOption:ZMQ_SUBSCRIBE];

/* Write to stdout immediately rather than at each newline.
* This makes the incremental temperatures appear incrementally.
*/
(void)setvbuf(stdout, NULL, _IONBF, BUFSIZ);

/* Process updates. */
NSLog(@"Collecting temperatures for zipcode %s from weather server…", filter);
const int kMaxUpdate = 100;
long total_temp = 0;
for (int update_nbr = 0; update_nbr < kMaxUpdate; ++update_nbr) {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

NSData *msg = [subscriber receiveDataWithFlags:0];
const char *string = [msg bytes];

int zipcode = 0, temperature = 0, relhumidity = 0;
(void)sscanf(string, "%d %d %d", &zipcode, &temperature, &relhumidity);

printf("%d ", temperature);
total_temp += temperature;

[pool drain];
}
/* End line of temperatures. */
putchar('\n');

NSLog(@"Average temperature for zipcode '%s' was %ld degF.",
filter, total_temp / kMaxUpdate);

/* [ZMQContext sockets] makes it easy to close all associated sockets. */
[[ctx sockets] makeObjectsPerformSelector:@selector(close)];
[pool drain];
return EXIT_SUCCESS;
}