c # fonksiyon tanımlama problemi

using System; 
  using System.Collections.Generic; 
  using System.Linq; 
  using System.Text; 
  using System.Collections; 
   
  namespace ConsoleApplication1 
  { 
      class Program 
      { 
          static void Main(string[] args) 
          { 
              ArrayList arrinsan = insanyarat(); 
   
              InsanAra(arrinsan, 'a'); 
          } 
          public static ArrayList insanyarat() 
          { 
              ArrayList arrNewinsan = new ArrayList(); 
              insan h = new insan("Can", "İskeçeli", 22); 
              arrNewinsan.Add(h); 
              insan h1 = new insan("Cemal", "Nalga", 22); 
              arrNewinsan.Add(h); 
              insan h2 = new insan("Cenk", "Kabadayı", 25); 
              arrNewinsan.Add(h); 
              insan h3 = new insan("Lady", "Gaga", 24); 
              return arrNewinsan; 
   
          } 
          public static void InsanAra(ArrayList insanlar, char ilkharf) 
          { 
              foreach (insan h in insanlar) 
              { 
                  if (h.Name[0] == ilkharf) 
                  { 
                      h.yazdir(); 
                  } 
              } 
   
          } 
   
   
      } 
   
   
  } 
   
  

using System; 
  using System.Collections.Generic; 
  using System.Linq; 
  using System.Text; 
   
  namespace ConsoleApplication1 
  { 
      class insan 
      { 
          public string Name; 
          public string Surname; 
          public int Age; 
          public insan(string name, string surname, int age) 
          { 
              Name = name; Surname = surname; Age = age; 
   
          } 
          public void yazdir() 
          { 
              Console.WriteLine("dsfsd"); 
          } 
   
   
   
     
      } 
  }