double radians(double degrees){    return degrees * M_PI / 180.0;}- (void)testDistance{    FMDatabase *db = [FMDatabase databaseWithPath:_writableDBPath];    if (![db open]) {        return;    }    [db makeFunctionNamed:@"distance" maximumArguments:4 withBlock:^(sqlite3_context *context, int argc, sqlite3_value **argv) {        double values[4];                // get the double values for the four arguments                for (int i = 0; i < 4; i++) {            int dataType = sqlite3_value_numeric_type(argv[i]);                        if (dataType == SQLITE_INTEGER || dataType == SQLITE_FLOAT) {                values[i] = sqlite3_value_double(argv[i]);            } else {                sqlite3_result_null(context);                return;            }        }                // let‘s give those values meaningful variable names                double lat  = radians(values[0]);        double lng  = radians(values[1]);        double lat2 = radians(values[2]);        double lng2 = radians(values[3]);                // calculate the distance                double result = 6371.393 * acos(cos(lat2) * cos(lat) * cos(lng2 - lng) + sin(lat2) * sin(lat));                sqlite3_result_double(context, result);    }];        int rowCount = 0;    FMResultSet *rs = [db executeQuery:@"SELECT *,distance(lat,lng,34.27344,108.95996) AS distance FROM hotel WHERE cityId = 10 AND lat > 33.27344 AND lat < 35.27344 AND lng > 107.95996 AND lng < 109.95996 ORDER BY distance ASC LIMIT 10"];        while ([rs next]) {        rowCount++;        NSLog(@"Does %@,%@ ", [rs stringForColumnIndex:1],[rs stringForColumn:@"distance"]);    }}