Count Leap year between Two Years

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Count the Years
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Calling Function
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var _nopl = NOPl(start.Year , last.Year);

  label4.Text=_nopl.ToString();

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Methode Like Delegate
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	 private static int NOPl(int start1, int last1)
        {
            var count = 0;
            
            for (var year = start1; year <= last1; year++)
            {
                count += DateTime.IsLeapYear(year) ? 1 : 0;

                
                
            }
            return count;
            

        }

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What are the Years
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Calling Function
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var _nop = NOP(start.Year, last.Year);

textBox4.Text = _nop.ToString();

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Methode Like Delegate
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private static int NOP(int start1, int last1)
        {
            int year = 0;
            //var count = 0;
            var yr=0;

            for (year = start1; year <= last1; year++)
            {
                if (Convert.ToBoolean(DateTime.IsLeapYear(year) ? 1 : 0))
                {
                    // count += DateTime.IsLeapYear(year) ? 1 : 0;
                    MessageBox.Show(year.ToString());
                   
                   
                    yr = year;
                   return yr;
                }
         }