Why am I getting this error: not all code paths return a value?

Question

hi im new to c# and was trying to code but getting error can anybody help me with this what am i doing wrong?

using System;
using System.Collections.Generic;
using System.Text;

namespace hodder
{
    class Program
    {
        public static void Main()
        {
            isHodder(3);
        }

        static int isHodder(int n)
        {
            int k = n;
            for (int i = 2; i <= n / 2;i++ )
            {
                if ((n % 1) == 0)
                {
                    return 0;
                }
                else
                {
                    for (int j = 2; j <= k;j++ )
                    {
                        if (n == (2^ j)  - 1)
                        {
                            return 1;
                        }
                        else
                        {
                            return 0;
                        }
                        k=(2^j)-1;
                    }
                }
            }
        }
    }
}

im getting error on " static int isHodder(int n) " 'hodder.Program.isHodder(int)': not all code paths return a value

and "Unreachable code detected " on "k=(2^j)-1"

Answer 1

The first error, "not all code paths return a value" means there is a path that the code could follow where no value would be returned (ie: calling isHodder(1)). You need to return some value outside of the for loop. Additionally, since you have an if/else block inside the second for loop the line

k=(2^j)-1;

Will never be executed.

    static int isHodder(int n)
    {
        int k = n;
        for (int i = 2; i <= n / 2; i++)
        {
            if ((n % 1) == 0)
            {
                return 0;
            }
            else
            {
                for (int j = 2; j <= k; j++)
                {
                    if (n == (2 ^ j) - 1)
                    {
                        return 1;
                    }
                    else
                    {
                        return 0;
                    }
                    k = (2 ^ j) - 1;
                }
            }
        }
        return 0;
    }

Answer 2

This line is highly suspect:

if ((n % 1) == 0)

Answer 3

What happens if I call isHodder(1)? Which return statement do I reach?

We may never enter the for loop at all (or if we do enter it, the compiler can't be sure that we reach a return statement before we leave the loop).

Answer 4

@jalf: is correct about the case where 2 <= n/2 (i.e., 4<=n). You will never enter the for loop in that case, so you need the return after the for.

As @Kenny suggested,

if ((n % 1) == 0)

Is suspect. n % 1 always == n, so the condition will only be true when n == 0. However, it also looks like this might be a typo, since the condition does not test anything that varies within the loop. Did you mean

if ((n % i) == 0)

?