Warm-up exercises
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1. Make a "Hello world" program.

2. Working with command line arguments...
    a. print how many of them there are.
    b. print them in order line by line
    c. print them in order line by line, with sequence numbers
    d. print them in reverse order
    e. print their lengths
    f. supposing that they are all numbers...
        I. print their sum
        II. print only the even numbers
        III. print them in numerical order
    g. print them in alphabetical order
    h. print only those of which there are multiple copies

3. a. Make a Fibonacci function, using the recursive definition.
   b. Make another version that uses iteration.
   c. Make another version that returns all the numbers up to the given value in an array.

4. Print all divisors of the number given in the first command line argument.

5. a. Find the function that takes the square root of numbers.
   b. If you have learned about Newton's method, make your own version using it.

6. The command line arguments contains an expression in reverse Polish notation,
   which consists of the four basic operations and integers.
   Calculate the value of the expression.

   Example:         1 2 3 * +
   Result:          7           = (3 * 2) + 1