using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        IEnumerable<int> values = new int[] {-1, 0, 1};

        CheckValues(values, IsPositive);

    }

    private static bool IsPositive(int input)

    {

        return input > 0;

    }

    private static void CheckValues(IEnumerable<int> values, Predicate<int> predicate)

    {

        foreach (int value in values)

        {

            bool isPositive = predicate(value);

            Console.WriteLine($"{value} {(isPositive ? "is" : "is not")} positive");

        }

    }

​

    private static void CheckValues(IEnumerable<int> values, Func<int, bool> predicate)

    {

        foreach (int value in values)

        {

            bool isPositive = predicate(value);

            Console.WriteLine($"{value} {(isPositive ? "is" : "is not")} positive");

        }

    }

}