• Day 3

• Purpose Day 3

• Understand the basic concepts of programming
• Be able to create a basic computer program
  

• Introduction to Programming  with Scratch

  
  
  
  

  But First

• What is an algorithm

• a process or set of rules to be followed in calculations or other problem-solving operations, especially by a computer.   https://en.wikipedia.org/wiki/Algorithm
  

• What is programming

• Converting an algorithm into a specific set of rules/steps for a specific computer or computer programming language.
  
  
• Most computer programming  languages have the following sets of rules
  
• Sequence
  
• Selection
• Iteration
  
  
  
• Sequence
  
• assignment of variables
• ask for input
• do calculations
• display output 
  
  
  
  and
  
  
  
  Scratch Example of Sequence
  
  
• Let's Build it - sequence
  
  
  
• Selection
• compare a value to another value
• do something else depending on the comparison
  
  
  Scratch Example of Selection
  
  
• Let's Build it - sequence and selection
  
  
  
• Iteration
• do something over and over until some condition is met, or possibly forever
  
  
  Scratch Example of Iteration
  
  
• Let's Build it - sequence selection and iteration.
  

Who can describe:

1. Sequence
2. Selection
3. Iteration

Let's flash a light with scratch.

Introduction to programming Python

• Examples of sequence, selection and iteration in python.
  
  
• Hello world  Sequence
  
  
  print ("hello, world")


• Let's Build it - sequence   Copy the above code and run it.

• Hello world with the appropriate greeting - selection
  
  
  # include the time library
  import time;
  
  # get the time in local time, specifically # the hour
  localtime = time.localtime (time.time())
  hour = localtime[3]
  
  #  Test the hour to find out what greeting to use.
  if hour < 6:
      print ("good night world")
  
  elif hour >=6 and hour < 12:
      print ("good morning world")
  
  elif hour >= 12 and hour < 18:
      print ("good afternoon world")
  
  elif hour >= 18 and hour < 24:
      print ("good evening world")

• Let's Build it - sequence and selection Copy the above code and run it.
  
  
• Hello world 10 times  - iteration
  
  
  for x in range(10):
      print ("hello, world")
  



# Ask for a number and then convert to a number.
count = int(raw_input("Enter a number"))
while count >= 0:
    print ("hello, world")
    count = count - 1

• Let's Build it - sequence and iteration. Copy the above code and run it.
  
  
• Blink the light - we did that above.  Now let's understand the program.
  
  
  
  #! /usr/bin/python
  
  # Flash a LED
  # Import the libraries we need
  import RPi.GPIO as GPIO
  import time
  
  # Set the pin mode to Broadcom mode this time.
  GPIO.setmode (GPIO.BCM)
  pin = 17
  
  # Set the pin to be an output
  GPIO.setup (pin, GPIO.OUT)
  
  i=0
  
  # Loop turning it on and off
  while i < 10:
      GPIO.output (pin, 1)
      time.sleep (1)
      GPIO.output (pin, 0)
      time.sleep (1)
      i = i + 1
  
  # Set the pins back to default
  GPIO.cleanup ()
  
  
  
  

• Power off your Pi. Remember to shut it down safely.
  
  
• Add another LED and a resistor.  Connect it to gpio pin  27.
  
• Then blink the two LEDs sequentially.
• Algorithm
1. turn LED 1on
2. wait a second
3. turn LED 1 off
4. turn LED 2 on
5. wait a second
6. turn LED 2 off
   
7. Go to step 1
   
   
• See if you can write the python code do do this.  Start with the above code
• Let's Build It. 
  
  
• If you have time add a third resistor and LED.
  
  
  How is programming in Python Different from Scratch? 
  
  Why would we choose one language vs. the other?