(Turtle Graphics) The Logo Language, which is particularly popular among personal computer users, made the concept of turtle graphics famous. Imagine a mechanical turtle that walks around the room under the control of a C++ program. The turtle holds a pen in one of two positions up or down. While the pen is down, the turtle trace out shapes as it moves; while the pen is up, the turtle moves about freely without writing anything . In this problem you will simulate the operation of the turtle and create a computerized sketchpad as well.

     Use a 20-by-20 array floor that is initialized to zeros. Read commands from an array that contains them. Keep track of the current position of the turtle at all times and whether the pen is currently up or down. Assume that the turtle always starts as position 0,0 of the floor with its pen up. The set of turtle commands your program must process are shown in FIG 4.29.

     Suppose that the turtle is somewhere near the center of the floor. The following "program" would draw and print a 12 by 12 square and end with the pen in the up position.

FIG. 4.29 Turtle graphics commands.

Command	Meaning
1	Pen up
2	Pen down
3	Turn right
4	Turn left
5 , n	Move forward n spaces
6	Print 20-by-20 array
9	End of data (sentinel)

     2

     5 , 12

     3

     5 , 12

     3

     5 , 12

     3

     5 , 12

     1

     6

     9

     As the turtle moves with the pen down, set the appropriate element of the array floor to 1's. When the 6 command (print) is given, wherever there is a 1 in the array, display an asterisk or some other character you choose. Wherever there is a zero, display a blank. Write a program to implement the turtle graphics capabilities discussed here. Write several turtle graphics programs to draw interesting shapes. Add other commands to increase the power of your turtle graphics language.

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