class Test
    {
        public static void Main()
        {
            int a = 3;
            DoWork(a);
            Console.WriteLine("The value of a is " + a);        
        }
        
        public static void DoWork(int i)
        {
            i++;
        }
    }
The program will result in :    The value of a is 3

class Test
    {
        public static void Main()
        {
            int a = 3;        // must be initialized
            DoWork(ref a);    // note ref
            Console.WriteLine("The value of a is " + a);        
        }
        
        public static void DoWork(ref int i) // note ref
        {
            i++;
        }
    }
The program will result : The value of a is 4

class Test
    {
        public static void Main()
        {
            int a;        // may be left un-initialized
            DoWork(out a);    // note out
            Console.WriteLine("The value of a is " + a);        
        }
        
        public static void DoWork(out int i) // note out
        {
            i=4;
        }
     }

The program will result : The value of a is 4