CS 1020 - Winter 2013 - Class 3

  • Before class
       - setup Sciborg Grand Prix
       - bring prize
       - bring in 8-ball course
       - new groups

  • Sciborg Grand Prix!

  • Administrative
       - Save the date: Wednesday 1/30 2-5pm Final project Talent Show
       - Visit schools some afternoon?
          - Friday 1/18 or
          - Wednesday 1/23 or
          - Friday 1/25
       - During lectures, please don't work on your robots, code, etc.
       - course web page resources: use them!
          - keep up with the readings
          - notes posted online for each class
          - code examples from class posted in the resources section (and also generally available linked from the notes)

  • Handy board boot loader
       - sometimes the Handy boards will crash or freeze up
       - when this happens the fix is often to reinstall the boot load (basically the OS for the Handy board
       - there is a link under the "Resources" section of the course web page
          - follow the instructors
       - you'll have to reload your program after reinstalling the boot loader
       - if this doesn't fix it, you'll have to bug one of us since it's probably a bigger issue

  • Revisiting the print command
       - Last time we saw that you can print a single word using
          
          print "word

       - or print multiple words by enclosing them in square braces

          print [more than one word]

       - or print sensor values

          print (sensor 0)

  • type command
       - Sometimes you might want to print words AND sensor values
       - the way to do that is using the "type" command
       - when you use the print command, the next time a print command is issues it resets the line and starts from scratch
       - the type command doesn't do this!
       - instead, the type command displays some text on the screen, but the next type/print command simply appends on to what is already there
       - So, if you want to put a label and a sensor value on the screen you first type the label and then print the sensor value:

          type [sensor 0:] ; print the text "sensor 0:"
          print (sensor 0) ; adds the actual value of sensor 0

       - You can do multiple type statements in a row to continually concatenate things, but the last thing will always be a print:
          type "i
          type "like
          print "cs

  • top and bottom
       - if you notice, the LCD screen actually consists of two lines
       - by default, print and type modify the top line of the LCD display
       - to top and bottom commands change where the text should be printed, e.g.

          top
          print [i like cs]
          bottom
          type "a
          print "lot

  • say
       - the say command works similarly to the print command, but instead of printing on the LCD screen it prints to the right side of the console
       - this can be very useful for debugging

  • mathematical operators in Handy Logo
       - As I mentioned before, Handy Log supports the basic mathematical operators (+, *, /, \--remainder)
       - All math operators MUST be separated by a space:
          - 2 + 3 (GOOD)
          - 2+3 (BAD)
       - Using say, we can see the value of some of these:
          say 2 + 3
          say 3 * 4
          say 4 / 2
          say 5 / 2
          say 5 \ 2
          say 2 + 3 * 2
          say 2 * 3 + 2
          say 2 * (3 + 2)

       - Anything interesting from these examples?
          - integer division (i.e. 5 / 2 gives us 2)
          - evaluation happens left to right (operator precedence does NOT matter)
          - parenthesis does affect precedence

  • repeat
       - write a function that beeps twice:
       
          to double-beep
             beep
             wait 5
             beep
          end

       - write a function that beeps 4 times:

          to quad-beep
             repeat 4[
                beep
                wait 5
             ]
          end

       - write a function that beeps an arbitrary number of times based on how I call the procedure, e.g.
          
          multi-beep 10

          would beep 10 times

  • parameters
       - so far all of our procedures have just been shortcuts for executing other statements
       - parameters allow us to pass information to a procedure when we call it (like 10 above)
       - parameters is Handy Logo are specified in the same line where we declare the name of the procedure and are prepended by a ':'
          - you can have as many as you'd like
          - the name you give them (with the :) are then usable inside the program
       - Using parameters we can easily implement multi-beep

          to multi-beep :n
             repeat :n[
                beep
                wait 5
             ]
          end
       
       - Try and write these functions that use parameters
          - beep-greater-ten: beeps if the value called is great than 10
          - print-bottom: takes one parameters and prints it on the bottom of the screen
          - print-top-bottom: takes two parameters and prints the first on the top and the second on the bottom
          - print-sum: takes two numbers as parameters and adds them and prints them to the screen

  • returning values
       - parameters allow us to pass values to functions
       - we also may want to GET information back from our procedures
       - this is called "returning" a value
       - to do this we use the keyword "output"
          - when the procedure executes the output statement it finishes the procedure, so don't have any statements following it
       - For example, if we wanted to write a square procedure that squares a value:

          to square :num
             output :num * :num
          end

  • Look at the area_calculator.txt code
       - We can use procedure that return values in places where values are expected
       - the circle_area procedure calls the square procedure and then uses the value returned to calculate the area
       - the print_circle_area procedure calls the circle_area procedure and uses the value to display it
       - we can call the print_circle_area program from the HandyLogo.jar console with a radius to see it run:
          print_circle_area 10

  • code style

  • Light sensors
       - the light sensors record values from 0 to 255 from very light to very dark (though it's hard to get values much darker than 100 in any conditions where there's ambient light)   
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