CS 111 - 1/25/18

Data Types Continued

   Some operators do differeent things based on the Data Type


     x   =  y /  z

     f   =  5 / 9 * ( f - 32 )   would be wrong if integer division
                                     occurs (always gives zero)

     f   =  (f - 32) * 5 / 9 

When working with strings both + and * are defined

    word1 = "HellO"
    word2 = "There"

    word3 = word1 + word2

    word4 = word1 * 3

This idea is called operator "overloading"



Turtle Drawings

   Develop some basic programming skills

   We have a turtle which has a pen on its back.
     The give the turtle commands such as:
       - move forward
       - turn
       - set pen down
       - lift pen up

We will need to set up the proper environment for the drawings

   1.  Create the World
          earth = makeWorld()

   2.  Create the turtle(s) that live on the world
          t1 = makeTurtle ( earth )

Then we want to write code to perform the desired algorithm

     To draw a square, the turtle will need to
       - draw 4 sides of same length
       - turn 90 degrees between each side

  To move forward, use the forward() JES library function

     syntax:
       forward ( <turtleVariableName> , <distance> )

     code:
       forward ( t1, 175 )
       
  To turn X degrees in a clockwise direction, 
   use turn() JES library function

     syntax:  
       turn ( <turtleVariableName> , <degrees> )
  
     code:
       turn ( t1, 90 )

If wanting to draw a second square (or other shape), we may
   want to reposition the turtle to another location without
   drawing a line:  use the penUp() and penDown() JES functions

    syntax:
      penUp  ( <turtleVariableName> )
      penDown( <turtleVariableName> )

    code:
      # lift the pen up
      penUp ( t1 )

      # reposition the turtle so no line is drawn
      turn    ( t1, 270 )
      forward ( t1, 50 )
      turn    ( t1, 90 )
  
      # put pen back down on the paper
      penUDown ( t1 )


To change the color of the pen we will need to use the JES Library
    METHOD of setPenColor()

  But First:
   FUNCTIONS vs METHODS  
    syntax is different

    Unfortunately, somethings are written as FUNCTIONS, some as
      METHODS, some as BOTH.

    forward exists in the JES library as both a FUNCTION and a METHOD

      syntax as a FUNCTION:

        forward ( <turtleVariableName> , <distance> )

      syntax as a METHOD:

        <turtleVariableName>.forward ( <distance> )

      code as a FUNCTION:

        forward ( t1, 175 )

      code as a METHOD:

        t1.forward ( 175 )


  Now: the senPenColor() METHOD from the JES library

    syntax:

      <turtleVariableName>.setPenColor ( <color> )

   JES has some pre-defined colors including:
       black, white, blue, red, green

    code to change the turtle's pen to blue:

      t1.setPenColor ( blue )