char* converted = ConvertDoubleToStr(666654);
printf("Converted string: %s n", converted);
return 0;

char* ConvertDoubleToStr(double d)
{
    printf("Input: %lf nn", d);
    const int length = sizeof (double);
    char result[length] = " ";

    sprintf(result, "%g", d);
    printf("Double -> Str. : %s n", result);

    return result;
}