从列表中返回超出列表范围的索引的值 C#

Question

I have a list. If the value that you've entered is within that list - result will be returned. Even if value is outside the result's range - result will be returned because of mod %. It's really hard to explain my problem with words, so lets take a look at the code :

        List<int> list1 = new List<int>(){ 0, 1, 2, 3, 4, 5, 6 };
        int value = 3; // what's this number to us?
        string result = "";
        int starting_number = 3;

        if (value == list1[(list1.IndexOf(starting_number) + 2) % list1.Count()])
        { result = "yeah"; }
        else if (value == list1[(list1.IndexOf(starting_number) + 1) % list1.Count()])
        { result = "cool"; }
        else if (value == list1[(list1.IndexOf(starting_number) + 0) % list1.Count()])
        { result = "one"; }
        else if (value == list1[(list1.IndexOf(starting_number) - 1) % list1.Count()])
        { result = "noo"; }
        else {result = "oops cant find it"; }

• starting_number. This number is constant. All measurments are made in relation to this number.
• value - the value that we've entered. we need to get the result for this value
• result - just a string

That's how it works:

starting_number = 3, value = 2 => result = "noo" (because 2 = IndexOf(starting_number)- 1)

starting_number = 6, value = 0 => result = "cool" (6 + 1 = 0)

starting_number = 0, value = 6 => Error will occur. (0 - 1 = 6)

any ideas how to improve the code to get rid of this error? Basically I can grab values is they are "after" starting_number, but I cant grab them "before" starting_number.

• in case of (6 + 1 = 0) : list looks like this 6,0,1,2,3...

• in case of (0 - 1 = 6) : list should be this...4,5,6,0

if you have any questions please ask.. it's really hard to explain the problem with words, but I guess examples made it more clear.

how do you grab values that are below starting_number?

Answer 1

If I understand correctly, you want to map all integers to range 0 to Count-1 and your current formula is x % count which works only when x > 0 . Then if you want it to work for all values of x try this one (x % count + count) % count

Answer 2

Try use this code

list1[Math.Sign((list1.IndexOf(starting_number) - 1))*(list1.IndexOf(starting_number) - 1) % list1.Count()]