#import <Foundation/Foundation.h>
NSString *jsonString = @"{\"user\":[{\"role\": [1, 3, 4],\"address\":{\"city\": \"biejing\"}}]}";
int main(int argc, const char * argv[])
{
    @
autoreleasepool {        
        // insert code here...
        NSLog(@"Hello, World!");
        NSData *data = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
        NSError *err;
        NSMutableDictionary * dict = [NSJSONSerialization JSONObjectWithData:data
            options:NSJSONReadingMutableContainers
            error:&err];
        dict[@"user"][0][@"address"][@"city"] = @"Shanghai";
        NSLog(@"%@",dict);
    }
    return 0;
}