Day elapsed or day counter

I needed to do the same awhile ago and didnt find any shortcuts. thought I would share what i came up with. it works good for getting days passed between dates. It doesn't include leap year so once every 4 years, if the two dates are before and after the last leap the comparison is off. but it would be easy to add the adjustment if it matters to you.

 public static int daysSince2000(string datetimestring){
         int ret = 0;
         string[] sa = datetimestring.Split ("/"[0]);
         int d, m, y;
         int.TryParse(sa [1],out d);
         int.TryParse ( sa [0],out m);
         int.TryParse (sa [2].Substring (2, 2),out y);
         while(y>0){y--;ret+=365;}
         while(m>0){m--;ret+=months[m];}
         while(d>0){d--;ret+=1;}
         return ret;
     }
 
 
     public static int[] months = new int[]{
         31,//jan
         28,//feb
         31,//mar
         30,//apr
         31,//may
         30,//jun
         31,//jul
         31,//aug
         30,//sep
         31,//oct
         30,//nov
         31,//dec
     }; 
 
 
     public void Start (){
 
         string now = System.DateTime.Now.ToString ();
         string FutureExample = "01/30/2019 11:19:01 PM"; 
 
         int count1 = daysSince2000 (now);
         int count2 = daysSince2000 (FutureExample);
 
         print ("days passed between dates= " + (count2 - count1));
      }

ok thank you, and if i would like to read only the number of the day from string?

Example today is 23/11/2018 and i would read only the "23" from system.datetime.now?

Thank you!!