return and while in function

Question

This function accepting input and telling the user whether the input is number or not a number.

static string isnum()
{
        Console.WriteLine("Write a number please");
        string a = Console.ReadLine();
        string nums = "123456789";
        int cnt = 0;
        for (int i = 0; i < a.Length; i++)
        {
            for (int j = 0; j < nums.Length; j++)
            {
                if (a[i] == nums[j])
                {
                    cnt++;
                    break;
                }
            }
        }
        if (cnt == a.Length)
        {
            Console.WriteLine(a + "  is a number");
            return a;
        }
        else
        {
            Console.WriteLine(a + "  is not a number");
            return "";
        } 
}


isnum();

I would like this function to repeat herself if the input is not a number, till the input will be a number, and then to stop. This function working now, but she's working only one time. When I'm trying to add a while block to the function to make her run again and again till the input is number I'm getting the "not all code paths return a value" error.

is it because a "return" statement ends a function, and therefore prevent her to run again? how can I solve that?

Thank you very much!

Answer 1

You can fix this with creating a loop arround it and do not return when it's not a number.

static string isnum()
{
    // just loop forever.
    while (true)
    {
        Console.WriteLine("Write a number please");
        string a = Console.ReadLine();
        string nums = "123456789";
        int cnt = 0;
        for (int i = 0; i < a.Length; i++)
        {
            for (int j = 0; j < nums.Length; j++)
            {
                if (a[i] == nums[j])
                {
                    cnt++;
                    break;
                }
            }
        }
        if (cnt == a.Length)
        {
            Console.WriteLine(a + "  is a number");
            return a;
        }
        else
        {
            Console.WriteLine(a + "  is not a number");
            // don't return here
        }
    }
}