Note: C# method parameter

Parameter type of C# method:
1. By value : defualt type
    public int Add(int num1, int num2)
       ...
2. By reference by in&out value : use "ref"
    public void Add(int num1, int num2, ref result)    
       ...
3. By reference by out only : use "out"
    public void Add(int num1, int num2, out result)
       ...