1. Introduction

     : | Definition | Special feature - TURTLE | Its two types |

 2. Windows

     : | Knowledge of running LOGO | Tips in LOGO |

 3. Commands

     : | Basic LOGO Commands | More LOGO Commands |

 4. Procedures

      : | Some procedures in LOGO |

 5. Examples

      : |  Some Examples |

 6. Messages

     : | Print Command in LOGO |

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1. INTRODUCTION > Definition

1.1.1. Computer Graphics

We can instruct a computer to draw a graph or a picture or patterns or graphs. The pictures drawn by a computer are called as Computer Graphics.

How does a computer draw a picture? The computer screen consists of a number of dots called Pixels. Several pixels can be joined to form a line. Each pixel is identified by the screen co-ordinates (x, y) where x is in the horizontal axis (row) and y is the vertical axis (column) as shown in Fig. 1.1.1.

1.1.2. What is LOGO?

LOGO is a programming language used for drawing pictures. You need to know and learn the LOGO Commands to draw simple pictures. LOGO stands for Logic-Oriented Graphic-Oriented. 

LOGO has a pen called a TURTLE which can be instructed to draw pictures. Turtle in LOGO is called as a turtle because the first version of LOGO used an electronic robot which resembled a turtle. The turtle and a sample of pictures drawn using LOGO instructions can be shown in Fig. 1.1.2.  

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1. INTRODUCTION > Special Features

1.2.1. Turtle

The turtle carries a pen and when it moves according to the instructions given by you, it draw a line on the window screen. The turtle represents a cursor in LOGO. It show the position on the screen where your instructions will be carried out.

The turtle moves on the screen according to the instructions given to it and these instructions are called as commands or primitives.

The shape of TURTLE in MSW LOGO	The shape of TURTLE in PC LOGO
The pointed end of the turtle is called its head and the wide end is called as its tail. The turtle is like a shape of a triangle.	The head of the turtle and its tail are just exactly like a shape of a real turtle.

1.2.2. LOGO Screen

LOGO Screen is split into two parts:

   Main Screen

   Commander Window

1.2.2.1. Main Screen

Main Screen is also known as the Graphic Screen. It is the place to draw pictures or figures. The triangle shape in the centre of the Graphic screen is called Turtle.  Turtle moves on the screen according to the commands given by you. These commands are also known as primitives.

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1.2.2.2. Commander Window

The Commander Window is the place to give commands to the turtle. The Commander Window has three important components:-

   Command Input Box

          - It is where you type commands in and execute them by clicking on the <Execute> button

             or by pressing the <Enter> key on the keyboard.

        - It is located in the bottom left portion of the Commander Window.

    Output or Command-Recall List Box

          - Displays and records all the commands that are executed and also any messages which are

           output as a result of these commands.

        - It is located above the Command Input Box.

    Execute button

        - Similar like the <Enter> button on the keyboard.

How does the Commander Window work out?

Command Input Box is linked to the Output/Command-Recall List Box. If you click on a line in the Output/Command-Recall List Box, it is automatically appeared in the Command Input Box. It can be executed by clicking on the <Execute> button or by pressing the <Enter> key on the keyboard.

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1. INTRODUCTION > Its two types

1.3.1. MSW Logo

Below is a symbol icon of MSW Logo Software.

FEATURES IN MSW LOGO

Microsoft Window LOGO In the MENU bar, it has got only 5 pop-up windows The shape of TURTLE is a like a shape of a 'triangle' LESS varieties in the window

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1.3.2. PC Logo

Below is a symbol icon of PC Logo Software.

FEATURES IN PC LOGO

IBM LOGO In the MENU bar, it has got 7 pop-up windows The shape of TURTLE is a like a shape of a 'real turtle' MORE varieties in the window

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1.3.3. The Similarities Between MSW Logo & PC Logo

  Some funtions in the window are SIMILAR

  Have pens called as TURTLE

  The process is the SAME

  SAME purpose i.e. used to draw pictures or graphics

2.0. WINDOWS > Knowledge of running LOGO

2.1.1. How to start LOGO?

STEP 1 : Click on <Start> button on the Windows Desktop. Start menu appears.

STEP 2 : Move the mouse pointer to <Programs>. Programs menu appears.

STEP 3 : Move the pointer to <Microsoft Windows Logo> or <PC Logo> (which ever LOGO type you wish to use) in the Programs menu. A submenu appears.

STEP 4 : Click on <MSW Logo> or <PC Logo> (which ever LOGO type you wish to use).

2.1.2. How to enter Commands?

To give a command to the turtle:

STEP 1 : Click on the Input box in the Commander Window.

STEP 2 : Type the command you wish to use.

STEP 3 : Press the <Enter> key from the keyboard or click on the <Execute> button in the Commander Window.

2.1.3 How to end LOGO Session?

After completing you work in LOGO, follow these steps to close the LOGO Window:

Type <BYE> in the Input box and press <Enter> key.

OR

Click on <Close> button on the top right corner of the Main screen.

The LOGO screen will be disappeared.

2.1.4 How to run LOGO?

Running the LOGO Language is very simple.

STEP 1 : Turn on the power supply to the computer and the monitor.

STEP 2 : Take a LOGO diskette and insert it into drive A or <A:>

STEP 3 : Wait until the computer displays the turtle in the center of the screen with a question mark (?) at the bottom left corner of the screen. The question mark is a prompt, indicating that LOGO is ready to accept your instructions.

REMEMBER: You must write each instruction on a separate line. When you have completed writing all the necessary instructions, you have written a LOGO program.

OR

You can download directly from http://www.softronic.com for MSWLogo Version 6.4 for Microsoft Windows 3.x/9x/NT. and do not forget to save in your programs file. It is a freeware software and can be downloaded free of cost.

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2.0. WINDOWS > Tips in LOGO

2.2.1. Tip 1

STEP 1 : Click on <Start> button on the Windows Desktop. Start menu appears.

STEP 2 : Move the mouse pointer to <Programs>. Programs menu appears.

STEP 3 : Move the pointer to <Microsoft Windows Logo> or <PC Logo> (which ever LOGO type you wish to use) in the Programs menu. A submenu appears.

STEP 4 : Right-Click on <MSW Logo> or <PC Logo> (which ever LOGO type you wish to use), then a pop-up window will appear. Click <Send To> and then click again <Desktop (Create Shortcut)>.

So that, in the future; you can directly open the LOGO Software on the <Desktop Window> immediately.

2.2.2. Tip 2

To type a command:

If you use lowercase DO NOT EVER mix it up with uppercase letters or vice-versa!!

Use [uppercase letter] ALL-THE-WAY-LONG for the command in the line.

 OR

use [lowercase letter] ALL-THE-WAY-LONG for the command in the line.

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3.0. COMMANDS > Basic LOGO Commands

3.1.1. Command 1

Command: <FORWARD> or <FD> Function: The forward command is used to move the turtle forward while drawing a line. Syntax: FD <number of steps> Example: FD 45 <Enter> Result: Draws a 45 steps long line in the forward direction.

3.1.2. Command 2

Command: <BACK> or <BK> Function: The back command is used to move the turtle backward while drawing a line. Syntax: BK <number of steps> Example: BK 40 <Enter> Result: Draws a 40 steps long line while moving backwards.

3.1.3. Command 3

Command: <RIGHT> or <RT> Function: Turns the turtle to its right through the specified number of degrees. Syntax: RT <number of degrees> Example: RT 90 <Enter> Result: Turns the head of the turtle by 90° to its RIGHT.

3.1.4. Command 4

 

Command: <LEFT> or <LT> Function: Turns the turtle to its left through the specified number of degrees. Syntax: LT <number of degrees> Example: LT 45 <Enter> Result: Turns the head of the turtle by 45° to its LEFT.

3.1.5. Command 5

Command: <PENUP> or <PU> Function: The PU command lifts the turtle's pen so that, it does not draw a line while moving. Syntax: PU <Enter>

3.1.6. Command 6

Command: <PENDOWN> or <PD> Function: The PD command puts the turtle's pen down so that it again starts drawing while moving. PD command is given only after PU command has already been used. Syntax: PD <Enter>

3.1.7. Command 7

Command: <HIDETURTLE> or <HT> Function: HT command hides the display of the turtle. Syntax: HT <Enter>

3.1.8. Command 8

Command: <SHOWTURTLE> or <ST> Function: ST command is used to display the turtle on the screen. It can be used only after the HT command has been used. Syntax: ST <Enter>

3.1.9. Command 9

Command: <CLEARSCREEN> or <CS> Function: CS command erases all the drawings on the scren and clears the Main screen or the Graphics screen, and also brings the turtle to the centre of screen. Syntax: CS <Enter>

3.1.10. Command 10

Command: <REPEAT> Function: REPEAT command allows to repeat a set of commands many times without writing them again and again. Syntax: REPEAT <n> [Set of commands] <Enter>, where n is the number of times a set of commands has to be repeated. Example: REPEAT 4 [FD 40 RT 90] Result: The REPEAT command will run the commands FD 40 & RT 90 four times to complete the SQUARE.

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3.0. COMMANDS > More LOGO Commands

3.2.1. More Command 1

Command: <FENCE>

Function: At times, you might give a command for the turtle to move which will take it beyond the screen. The <FENCE> command creates a fence around the screen so that the turtle cannot go beyond the screen.

Syntax: FENCE <Enter>

Example:

FENCE <Enter>

RT 80 <Enter>

FD 600 <Enter>

Result: A message Turtle out of bounds appears and the figure is displayed, truncated at the right end of the screen.

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3.2.2. More Command 2

Command: <WRAP>

Function: The <WRAP> command allows the turtle to reappear on the other end of the screen once the edge is reached.

Syntax: WRAP <Enter>

Example:

WRAP <Enter>

RT 80 <Enter>

FD 600 <Enter>

Result: When the screen is in Wrap Mode, as the edge of the screen is reached, turtle appears at the other end, drawing the balance part of picture.

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3.2.3. More Command 3

Command: Nested <REPEAT> (Repeat within Repeat)

Function: The REPEAT command when given inside another REPEAT command.

Example 1:

REPEAT 2 [REPEAT 4 [FD 40 RT 90] RT 90] <Enter>

Result: Two squares are shown in the figure below.

Example 2:

REPEAT 2 [REPEAT 6 [FD 80 RT 60] RT 120] <Enter>

Example 3:

REPEAT 2 [REPEAT 8 [FD 30 BK 30 RT 45] PU FD 40 PD] <Enter>

Example 4:

REPEAT 12 [REPEAT 6 [FD 40 LT 60] RT 30] <Enter>

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4.0. PROCEDURES > Some Procedures in LOGO

4.1.1. What is A Logo Procedure?

In LOGO, the commands are executed as and when entered. These commands do not get stored in memory.

Till now we have been writing commands one by one to draw figures. If the same figure is to be drawn again, the same set of commands will have to be given again. Instead, if we want to save the set of commands and give it a name, we can do it with the help of LOGO Procedures.

A procedure is useful if we want to reuse a certain set of commands. We can give a name to a set of commands and can recall it whenever needed. A procedure once defined can be stored in memory and can be called any time when required.

A LOGO procedure is a set of LOGO commands given one after the other to perform a particular task and referred to by a name.

A LOGO Procedure is divided into 3 parts:

  Title of the Procedure

  Set of Instructions

  End Line

The Title of the Procedure:

Can include letters, numbers or symbols

The first character should always be a letter

Blank spaces cannot be included

Arithmetic operators + , -, *, / cannot be included in the name

LOGO Command names cannot be included

The title of the procedure is the name given to the procedure. Preferably a procedure name should be such that it gives some information about the set of instructions.

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4.1.2. Writing A Procedure

WRITING A PROCEDURE USING THE INPUT BOX:

STEP 1 : Click in the Command Input Box

STEP 2 : Type <TO> followed by a name for the procedure, for example: TO CIRCLE

STEP 3 : Now, press the <Enter> key

STEP 4 : After pressing the <Enter> key, the To Mode Input box appears

STEP 5 : Click inside the box

STEP 6 : Enter the commands one after the other, pressing the <Enter> key after each command

STEP 7 : Type <END> to mark the end of the procedure

WRITING OR EDITING A LOGO PROCEDURE USING THE EDITOR WINDOW:

The Editor Window allows you to make changes in an already existing procedure and also to write new procedures.

To write a new procedure using Editor Window follow the steps given below:

STEP 1 : Click in the Command Input box and type <Edit "Square"> and press the <Enter> key. Square is the name of a new procedure. The Editor Window appears as shown below.

STEP 2 : Insert a blank line after the line containing TO SQUARE by pressing <Enter> key.

STEP 3 : Type the commands that you want to be included in the procedure for example,

CS

FD 40

RT 90

FD 40

RT 90

FD 40

RT 90

FD 40

The commands appear in the Editor Window between the Title Line and the End Line.

STEP 4 : Click on <File> in the Menu bar of the Editor window.

STEP 5 : Click on <Save and Exit> option in the Dropdown menu.

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4.1.3. Running A Procedure

Running a procedure, means executing the set of commands typed and saved in the procedure. A defined procedure can be called any time by simply typing the name of the procedure in the Command Input box.

You can run a procedure by typing the name of the procedure, for example, SQUARE in the Command Input box and then pressing the <Enter> key.

4.1.4. Variables

A variable in LOGO is denoted by a: , followed by the name of the variable. For example,

TO VARYSQ :SIDE

REPEAT 4 [FD :SIDE RT 90]

END

Now, lets do on your own with these examples:

EXAMPLE 1 TO VARYRECT :W :L REPEAT 2 [FD :W RT 90 FD :L RT 90] END	EXAMPLE 2 TO HEXAGON :SIDE REPEAT 6 [FD :SIDE RT 60] END
EXAMPLE 3 TO POLY :SIDE :ANGLE REPEAT 360/:ANGLE [FD :SIDE RT :ANGLE] END	EXAMPLE 4 TO ROTATE :SIDE :ANGLE REPEAT 360/:ANGLE [POLY :SIDE :ANGLE LT 90] END

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4.1.5. Examples

Now, let us look at a few examples of procedures:

EXAMPLE 1

Procedure to draw a SQUARE:

TO SQUARE

REPEAT 4 [FD 40 RT 90]

END

SQUARE DEFINED

To run the procedure, type <SQUARE> and press the <Enter> key.

A square gets drawn on the Graphic screen as shown.

EXAMPLE 2

Procedure to draw a CIRCLE:

TO CIRCLE

REPEAT 360 [FD 1 RT 1]

END

CIRCLE DEFINED

To run the procedure, type <CIRCLE> and press the <Enter> key.

A circle is drawn in the Graphic Screen.

EXAMPLE 3

Procedure to draw a TRIANGLE:

TO TRIANGLE

REPEAT 3 [FD 60 RT 120]

END

TRIANGLE DEFINED

To run the procedure, type <TRIANGLE> and press the <Enter> key.

Then a triangle is drawn in the Graphic Screen.

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5.0. EXAMPLES > Some examples

5.1.1. EXAMPLE 1

PROBLEM: To draw a Computer

PLANNING: Draw a BOX chart

CODING THE PROGRAM:

SAMPLE RUN: Type <COMPUTER>

5.1.2. EXAMPLE 2

PROBLEM: To draw a Rocket

PLANNING: Draw a BOX chart

CODING THE PROGRAM:

SAMPLE RUN: Type <ROCKET>

5.1.3. EXAMPLE 3

PROBLEM: To draw a Butterfly

PLANNING: Draw a BOX chart

CODING THE PROGRAM:

SAMPLE RUN: Type <BFLY>

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6.0. MESSAGES > Print command in LOGO

6.1.1. Why do you need to print messages in LOGO?

You have drawn shapes and figures by moving the turtle with the help of various LOGO commands. But you cannot use these commands to write any text or message on the screen. Neither can you use these commands to carry out calculations like addition and subtraction on numbers.

Sometimes you may want to write some messages or solve sums. LOGO provides you commands to do so. You will learn how to print text messages on the screen using the <PRINT> Command.

6.1.2. PRINT Command

The <PRINT> command in LOGO is used to print a text on the screen. The short form of PRINT is PR. Message to be printed can consist of one or more words or even a sentence.

The syntax of PRINT command is:

PRINT "word

or

PRINT [sentence]

PRINTING A WORD

If you want to print a single word, the primitive name should be followed by an opening quotation mark before the word to be printed.

Example: PRINT "LOGO

On executing this command the word LOGO gets printed in the Commander Window.

PRINTING A SENTENCE

For displaying a message in the form of a sentence, the message to be displayed should be included within a pair of square brackets.

Example: PRINT [Welcome to the World of LOGO]

This command displays the sentence written within the square brackets in the Output/Command-Recall List box.

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