if (ProductNameArray.Any(usersearch.Contains))

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

namespace Prac_Test3
{


class Program
{
     // Constants
        const int SIZE_OF_PRODUCT_CODE = 4;
        const float CATEGORY_A_MARKUP = 10.0F;
        const float CATEGORY_C_MARKUP = 33.3F;
        const float CATEGORY_P_MARKUP = 15.0F;
        const int ARRAY_SIZE = 100;


    static void DisplayMenu()
    {
        Console.Clear();
        Console.WriteLine("--------------> Menu <------------");
        Console.WriteLine("1. Add a product                (a)");
        Console.WriteLine("2. Find a product               (f)");
        Console.WriteLine("3. Enter the quantity in stock  (q)");
        Console.WriteLine("4. Delete a product             (d)");
        Console.WriteLine("5. Calculate and display values (v)");
        Console.WriteLine("6. Exit                         (x)");
        Console.Write("rnEnter your selection: ");
    }
    static void AddProduct( string[] ProductNameArray, string[] ProductCodeArray, float[] WholesalePriceArray, ref int NextAvaliablePosition)
    {
        string ProductName = "";
        string ProductCode = "";
        string ProductCategory = "";

        float WholesalePricePerItem = 0.0F;

        bool ParseResult = false;
        bool ErrorFlag = false;

        string UserResponse = "";

        do
        {
            ErrorFlag = false;
            Console.Write("Product Name                : ");
            ProductName = Console.ReadLine();
            if (ProductName == "")
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine("Product Name must not be left blank.");
                Console.ForegroundColor = ConsoleColor.Gray;
                ErrorFlag = true;
            }
        } while (ErrorFlag);

        do
        {
            ErrorFlag = false;
            Console.Write("Product Code                : ");
            ProductCode = Console.ReadLine();
            if (ProductCode == "")
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine("Product Name must not be left blank.");
                Console.ForegroundColor = ConsoleColor.Gray;
                ErrorFlag = true;
            }
            else if (ProductCode.Length != SIZE_OF_PRODUCT_CODE)
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine("Product Code must be exactly four characters.");
                Console.ForegroundColor = ConsoleColor.Gray;
                ErrorFlag = true;
            }
            else
            {
                ProductCategory = ProductCode.Substring(0, 1);
                ProductCategory = ProductCategory.ToUpper();
                if (ProductCategory != "A" && ProductCategory != "C" && ProductCategory != "P")
                {
                    Console.ForegroundColor = ConsoleColor.Red;
                    Console.WriteLine("Product Code must start with A, C or P.");
                    Console.ForegroundColor = ConsoleColor.Gray;
                    ErrorFlag = true;
                }
                else if (!(Char.IsDigit(ProductCode[1])) && !(Char.IsDigit(ProductCode[2])) && !(Char.IsDigit(ProductCode[3])))
                {
                    Console.ForegroundColor = ConsoleColor.Red;
                    Console.WriteLine("Product Code  must be A, C or P followed by three digits.");
                    Console.ForegroundColor = ConsoleColor.Gray;
                    ErrorFlag = true;
                }
            }
        } while (ErrorFlag);

        do
        {
            ErrorFlag = false;
            Console.Write("Wholesale price per item ($): ");
            UserResponse = Console.ReadLine();
            ParseResult = float.TryParse(UserResponse, out WholesalePricePerItem);
            if (ParseResult == false)
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine("Not a valid number.");
                Console.ForegroundColor = ConsoleColor.Gray;
                ErrorFlag = true;
            }
            else if (WholesalePricePerItem <= 0)
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine("Wholesale price must be a number greater than 0.");
                Console.ForegroundColor = ConsoleColor.Gray;
                ErrorFlag = true;
            }
        } while (ErrorFlag);
    }
    static void FindProduct(Array ProductNameArray)
    {

        int search = -1;
        string usersearch;

        usersearch = Console.ReadLine();
        search = Array.IndexOf(ProductNameArray, usersearch);

        if (search >=0)
        {
            if (ProductNameArray.Any(usersearch.Contains))
            {
                Console.WriteLine(" details blah blah");
            }
        }
        else if (search <0)
        {
            Console.WriteLine("No record exists.");
        }

if (ProductNameArray.Cast<string>().Any(usersearch.Contains))

static void FindProduct(Array ProductNameArray)

static void FindProduct(string[] ProductNameArray)

namespace Your.Namespace
{
    using System;
    using ... // your other usings
    using System.Linq;

    public sealed class YourClass
    {
        public void Test()
        {
            // ...
            yourArray.Any()
        }
    }
}

using System.Linq;