= Functions

* Today I will do a lesson on functions.

== Functions
* What is a function?
* Benefits of functions?
* How are functions used?
* How to make a function (see examples below)

== Code Example
* Here is an example:

<Code:Python>
def main():
    x = 5
    y = 12
    z = add(x, y)
    print(z)    

def add(a, b):
    c = a + b
    return c

if __name__ == "__main__":
    main()
</Code>

* There are three parts.
** One, "def main()" creates the main() function.
** Two, "def add(a, b)" creates a function with two arguments, or, parameters.
** Three, "if __name__ == main...." means, to run the "main" function first.

So you see, you can use the add() function to add numbers.

== Homework
* Classwork/Hommework: Students must: 
** Write a function to multiply two numbers.
** Write a function to divide two numbers.
** Write a function to subtract two numbers.
** Test the program! //(How do you  test? use print() to show the answer.)//

=== Advanced
Is this too easy? Here are some more challenging questions:

* Write a function that returns a random number.
* Write a function that returns a random fruit name.

or maybe,
* Write a function that prints "even" or "odd" if the number is even or odd.

<Code:Python|Example answer!>
def isEven(a):
    x = a // 2      #NOTE: / always returns a float. // always returns the lowest integer!
    if a == x:
        return "even"
    else:
        return "odd"
</Code>

There are many, many ways to do this. The students should be able to think of at least this:

<Code:Python|Example answer 2!>
def isEven(a):
    while a >= 2:
        a = a - 2
        
    if a == 0:
        print("even")
    else:
        print("odd")
</Code>

If this challenge is too easy, they can always write a function that determines if a number is prime.