Objective-c when to release objects

-(IBAction)registerUpdate:(id)开发者_StackOverflowsender {
    HTTPRequest* request = [[HTTPRequest alloc] initWithUrl:@"http://www.yahoo.com" delegate:self];
    [request doRequest];
}

The HTTPRequest makes an asynchronous request and calls the onHTTPResponse method in the current class.

My question is do I have to release request? My guess is that I'm supposed to make it an instance variable?

[NSString stringWithFormat:@"Data received: %@", [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding]];

How would I release that string object, or should I assign it to a variable?

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You release it with autorelease

[NSString stringWithFormat:@"Data received: %@", [[[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding] autorelease]]