NSMutableArray *array= [NSMutableArray arrayWithObjects:@"1", @"2",@"3",@"4", nil];
NSData *jsond = [NSJSONSerialization dataWithJSONObject: array options:NSJSONWritingPrettyPrinted error:NULL];
NSString *json = [[NSString alloc] initWithData:jsond encoding:NSUTF8StringEncoding];

NSLog(@"%@", json);