Background
jLogo Programming
 Commanding a Turtle
 Pseudocode
 Adding New Commands
 Iteration & Animation
 Hierarchical Structure
 Procedure Inputs
 Operators & Expressions
 Defining Operators
 Words & Sentences
 User Interface Events
 What If? (Predicates)
 Recursion
 Local Variables
 Global Variables
 Word/Sentence Iteration
 Mastermind Project
 Turtles As Actors
 Arrays
 File Input/Output
Java
 A Java Program
 What's a Class?
 Extending Existing Classes
 Types
 Turtle Graphics
 Control Flow
 User Interface Events
Appendices
Updates
 December 13, 2008
 January 6, 2012
 March 15, 2013
 January 20, 2014
 February 13, 2014
 July 29, 2014
 January 18, 2016
 January 29, 2016
Lastly
Two New Builtin Operators  Why?
In the GridToolkit, I used two builtin operators that you have not seen before. What are they? Why did I need to use them?
Answer:
The new builtin operators used are int and remainder. They are used in the procedure gridGotoCell.

INT
forward product gridCellSize (int quotient :idx gridNumCol)
What does it do? The expression "quotient :idx gridNumCol" is intended to produce the row number. The row number multiplied by the size of a cell is the distance the turtle needs to move southward (from the top of the grid) to arrive at the desired row. What int does is to remove the fractional part of its input, a number. Here is an example, a walkthrough, to show what's going on.
Let's say we want to go to the topleft corner of cell 12 in a grid that has 8 columns (gridNumCol = 8). Cell 12 is in the second row, so I'm going to need the turtle to move south from its position at the topleft corner of the grid a distance equal to the size of one cell. Well... quotient 12 8 produces 1.5 and striping off the fractional part gets us the value we need: 1. If we do not remove the fractional part, the turtle will move too far... past the top of the second row, to the middle of the cell's height.

REMAINDER
forward product gridCellSize (remainder :idx gridNumCol)
What does it do? The expression "remainder :idx gridNumCol" produces the column number. The column number multiplied by the size of a cell is the distance the turtle needs to move eastward to get to the desired column.
Let's extend the int walkthrough... At the point in the procedure where remainder is used (in a forward command), the turtle is positioned at the top of the desired row. First the turtle's heading it set to east. Then we need to move forward to the leftedge of the desired column. Since there are eight (8) columns in a row, when you divide the desired cell number twelve (12) by eight you get one (1) with a remainder of four (4). Four times the size of a cell gets the turtle to the leftside of the twelfth cell.