Sort the digits programming exercise.

The winter is coming, and all the warehouses are nicely packed with food. But someone needs to sort it all. So the king offers a noble title to anyone who can:

Write a function that takes an integer as an input. And then generates a new number where all the digits are sorted in an descending order.

Example:
1342 => 4321
5791 => 9751

Scroll down for the solution of this programming exercise.

    public static int SortDigits(int num)
    {
//Oh boy.. We can solve this coding problem
//in a 1000 different ways. But since the goal is
//to learn new things, I am going to use a lot of 
//functions and explain them.

//first lets convert "num" to string and then to char array.         
        char[] digits = num.ToString().ToCharArray();
//we needed this array so we can sort it.       
        Array.Sort(digits);
//but we need a reverse sorting
        Array.Reverse(digits);
//now we have a char array, but we need an integer

        string str = new string(digits);
        return int.Parse(str);
 //and that's how we convert char array to a string
 //I want to stress that we cannot use = operator
 //we cannot do "str=digits". Because they are different types
 //s is a string and digits is an array.
//Do be safe, assume that we can use the Assignment operator "=" 
//only on the same data types. 
    }