You can try with a framework such as this,https://github.com/stig/json-framework
Example usage would be, assuming userId is declared in your header file.
SBJSON *parser = [[SBJSON alloc] init];
NSArray *statuses = [parser objectWithString:json_string error:nil];
userId = [statuses valueForKey:@"userid"];
Now userId retains the value for the json value for userid from the json string
UPDATE: If you're only supporting iOS >= 5.0 I would suggest the built in NSJSONSerialization
class. If this is the case, your code will look more like this..
NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
NSMutableArray *jsonList = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:nil];
userId = [jsonList valueForKey:@"userid"];
NSLog(@"userid: %@", userId); // will print "Please enter correct Email Address"
Hope this helps !