Not all code paths return a value - Enum practice

Question

I've tried to execute a simple code just to study the enumeration topic. Yet, I've faced this issue: "Not all code paths return a value". Here is the code:

namespace ConsoleAppTest
{
    class Program
    {
        enum Seasons { Winter, Spring, Summer, Fall };

        static void Main(string[] args)
        {
            WhichSeason(3);
        }

        static Seasons WhichSeason(int month)
        {
            if (month >= 1 || month <= 3)
            {
                return Seasons.Winter;
            }
            else if (month >= 4 || month <= 6)
            {
                return Seasons.Spring;
            }
            else if (month >= 7 || month <= 9)
            {
                return Seasons.Summer;
            }
            else if (month >= 10 || month <= 12)
            {
                return Seasons.Fall;
            }
        }
    }
}

I wonder what could cause this problem. Thanks :)

Answer 1

You should handle the else case. Your month integer could also be <1 or >12.

static Seasons WhichSeason(int month)
{
    if (month >= 1 && month <= 3)
    {
        return Seasons.Winter;
    }
    else if (month >= 4 && month <= 6)
    {
        return Seasons.Spring;
    }
    else if (month >= 7 && month <= 9)
    {
        return Seasons.Summer;
    }
    else if (month >= 10 && month <= 12)
    {
        return Seasons.Fall;
    }
    else
    {
        throw new ArgumentOutOfRangeException("invalid month");
    }
}

so if you call

WhichSeason(13); //throws exception

Answer 2

What should be returned if month, say -1 or 123? You can solve the problem in two main ways, silent:

    // Please, notice "None"
    enum Seasons { None, Winter, Spring, Summer, Fall };

    static void Main(string[] args)
    {
        WhichSeason(3);
    }

    static Seasons WhichSeason(int month)
    {
        if (month >= 1 && month <= 3)
            return Seasons.Winter;
        else if (month >= 4 && month <= 6)
            return Seasons.Spring;
        else if (month >= 7 && month <= 9)
            return Seasons.Summer;
        else if (month >= 10 && month <= 12)
            return Seasons.Fall;
        else
            return Seasons.None;
    }

Or throwing appropriate exception, ArgumentOutOfRangeException in the case

    enum Seasons {  Winter, Spring, Summer, Fall };

    static void Main(string[] args)
    {
        WhichSeason(3);
    }

    static Seasons WhichSeason(int month)
    {
        if (month >= 1 && month <= 3)
            return Seasons.Winter;
        else if (month >= 4 && month <= 6)
            return Seasons.Spring;
        else if (month >= 7 && month <= 9)
            return Seasons.Summer;
        else if (month >= 10 && month <= 12)
            return Seasons.Fall;
        else
            throw new ArgumentOutOfRangeException(
              "month", 
              "month must be in [1..12] range."); // Exception
    }

Edit: I've preserved WhichSeason intact, but it seems that you have a logic error in the implementation and the right routine should be

    static Seasons WhichSeason(int month)
    {
        if (month >= 1 && month <= 2 || month == 12) // Jan, Feb and Dec 
            return Seasons.Winter;
        else if (month >= 3 && month <= 5) // Mar-May
            return Seasons.Spring;
        else if (month >= 6 && month <= 8) // Jun-Aug
            return Seasons.Summer;
        else if (month >= 9 && month <= 11) // Sep-Nov
            return Seasons.Fall;
        else
            return Seasons.None;
    }