using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Linearsearch2
{
    class Program
    {
        static void Main(string[] args)
        {
            var array = new int[] { 1, 31, 10, 9, 420, -5, 77, 420, 300, 99 }; //Sets up the array

            var targetvalue = 77; //Establishes what number the search will attempt to find.
            var targetpos = -1; //Establishes the position in the array of the target.
            var targetnumber = 0; //Establishes the counter for the number of times the target appears.
            bool found = false; //Decides wether to change the number or use a counter method.

            var foundpositions = new int[] { }; //Establishes an array which will hold the positions of located items

            for (var i = 1; i < array.Length; i++)
            {
                if (found == true && array[i] == targetvalue)
                {
                    targetnumber = targetnumber + 1;
                }

                if (found == false && array[i] == targetvalue) //If the target value has not been found yet
                {
                    foundpositions.Add(i); //This is the line i need help with. I dont know how to add a value to an array properly.
                    found = true;
                }
            }

            if (targetpos != -1){ //If the target number was found
                Console.WriteLine("The number " + targetvalue + " appeared " + targetnumber + " times, at positions " + foundpositions + "."); // Prints the final outcome.
            }
            else //If the target number was not found
            {
                Console.WriteLine("The number " + targetvalue + " did not appear in this array."); // Prints the final outcome.
            }
        }
    }
}

var foundpositions = new int[] { };

var foundpositions = new List<int>();

var targetpos = -1;

if (targetpos != -1){ //If the target number was found
      Console.WriteLine("The number " + targetvalue + " appeared " + targetnumber + " times, at positions " + foundpositions + "."); // Prints the final outcome.
}

public static int LinearSearch(int[] items, int target)
{
       if (items == null) throw new ArgumentNullException("argument items has null reference");
       if (items.Length == 0) return -1; // return -1 if the item is not found
       for (int i = 0; i < items.Length; i++)
            if (items[i] == target) return i;
       return -1; // return -1 if the item is not found
}

private static void FindTargets() {
  var array = new int[] { 1, 31, 10, 9, 420, -5, 77, 420, 300, 99, 1, 31, 10, 9, 420, -5, 77, 420, 300, 99 }; //Sets up the array
  int target = 77;
  List<int> foundTargets = GetPositions(target, array);
  StringBuilder sb = new StringBuilder();
  sb.Append("There are " + foundTargets.Count + " int(s) that match " + target + Environment.NewLine);
  sb.Append("The array indexs for the target ints " + target + " are: ");
  int count = 0;
  foreach (int curInt in foundTargets) {
    sb.Append(curInt);
    if (count < foundTargets.Count - 1)
      sb.Append(", ");
    count++;
  }
  Console.WriteLine(sb.ToString());
}

private static List<int> GetPositions(int target, int[] intArray) {
  List<int> foundTargets = new List<int>();
  for (int i = 0; i < intArray.Length; i++) {
    if (intArray[i] == target) {
      foundTargets.Add(i);
    }
  }
  return foundTargets;
}