CS 101 - 9/13/2011


When drawing a sqaure, we repeat the same steps 4 times.

Looping statements - allows some number of operations
   to be repeated some number of times.

while statement

    general form:

    while ( <expression> )
       {
         <operation(s)>
       }

    the <operation(s)> will continue to be executed
    while the <expression> exvaluated to TRUE

    Often we need to use the relational operator in
    our <expression>

      ==  equality
      !=  inequality (not equal)
      >   greater than
      >=  greater than or equal
      <   less than
      <=  less than or equal

  Example of a while loop

    int count;

    count = 1;

    while ( count <= 4 )
       {
         System.out.println ("Count: " + count);
         count = count + 1;
       }

When writing a loop, a common error is not having
the <expression> ever become FALSE.  This is called

   an Infinite Loop

When drawing a regular shape of X sides,
  each angle should be of 360/X degrees.

    Triangle (3 sides)  360/3 = 120
    Square   (4 sides)  360/4 = 90
    Pentagon (5 sides)  360/5 = 72
    Hexagon  (6 sides)  360/6 = 60

Computer Scientists count Strange!!!!

    They start counting from zero instead of one.
    So a loop that runs tens times normally appears
    as follows:

    count = 0;

    while ( count < 10 )
       {
         System.out.println ("Count: " + count);
         count = count + 1;
       }
    System.out.println ("Count after loop: " + count);


For the first project, we will be drawing on a picture.

When we create the turtle, we give the constructor
 a picture instead of a world.  So the next question
 is: How do we create a Picture.

When creating a picture we can create a blank 
  (all white) picture of whatever size we want
  with the Picture contructor 

      Picture (int width, int height);

Or open an existing Picture, with the constructor:
    
      Picture (String filename);