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Logo Instructions. Logo is a language developed for school children by Seymour Papert. It encourages them to interact more eagerly and more easily with the computer. The Logo language consists of two parts: there is the list handling section and the far more widely used Turtle Graphics section. It is the Turtle Graphics which you have here. Turtle Graphics will allow you to create a variety of different patterns on the screen as well as introduce you to good programming practice. In addition it will allow you to create an almost "intelligent" Turtle as well as use the Turtle to plot graphs. Logo is considered such an important language in allowing children to build up confidence in the computer that it is quoted in several places in the National Curriculum , Mathematics document. The version which you have purchased will allow you to do develop all the Logo ideas described in that document. Getting Started: Insert the disc in the logged disc drive, type LOGO and press return. The disc must have Logo.exe and Logo.dat in the same directory. All your files will also be stored in this directory. Now that you are into Logo you have the ? prompt. This is to remind you that you are now in charge of the Turtle- that is the little triangle in the middle of the screen. That is its Home and when you type Home that is where it will go. Now enter a command such as FORWARD 100 or FD 100 for short, and press return. This tells the Turtle to move forward by 100 steps. Commands can be in UPPER or lower case. All commands should have a space after them. We can make it turn right by 90 degrees with RIGHT 90 or RT 90. LEFT 27 or LT 27 will turn it 27 degrees to the left. Sometimes we don't want the Turtle to be visible. When invisible it does draw faster. We can hide the Turtle with HT and make it show again with ST. By now you know enough Logo to draw some simple patterns. Draw some. If you make a small mistake use PE to turn the Turtle pen into an eraser to rub out the line and then SETPC 15 to change it back into a pen that draws. If you make a terrible mess of the screen then type CLEAN to clean the screen. If you want to move the Turtle to a new spot on the screen without it drawing then use PU for pen up then use PD when you want it to draw again. The screen you are working on measures 2000 units by 2000 units. The centre of the screen has co-ordinates 0,0. You can use SETX -123 to put the Turtle at position X=-123 and SETY -234 to put it at position Y=-234. You can also use SETPOS -123 -234 to place the Turtle at the same position. To find out where you are on the screen type: PR POS The Turtle cannot leave the screen unless you give it permission. It sees a fence right round the screen. If you try and go FORWARD 3000 then it will say "That is over the fence." To allow the Turtle to escape you can use the command WRAP. This allows the Turtle to disappear of one side of the screen and immediately reappear on the opposite side of the screen. It is as if the screen were a sphere. The other method of letting the Turtle leave the screen is to give it the command WINDOW. This allows the Turtle to go anywhere but you can only see it when it appears in front of the window which is the screen. Now we can draw simple patterns. To draw a square you need the following commands: CS FD 200 RT 90 FD 200 RT 90 FD 200 RT 90 FD 200 RT 90 which is very slow to type every time you want a square. Instead we can reduce that to: CS REP 4[FD 200 RT 90] This is short for repeat four times the section in square brackets. This will produce a square. We can have brackets inside brackets. For example try: CS REP 4[FD 200 RT 90 REP 4[FD 80 LT 90]] Even that can be bit of a handful if we have to type it regularly so instead we can write a procedure. Procedures These can be thought of as short programs. To write a procedure to draw a square type: TO Square and press return. The prompt has changed from a ? to a > showing you that you are in the editor and not controlling the Turtle. Enter the lines : REP 4[FD 100 RT 90] END The last line has told the computer that you have finished with the editor and you now wish to have control over the Turtle again You could have just pressed return rather than type the word end. This time to draw that square all you have to do is to type Square and the Turtle will carry out the procedure Square. We can demonstrate this with: CS REP 18[Square RT 20 FD 40] You could have called it any name you wanted to but square seems sensible. It is possible to make further improvements to this procedure. This time enter: TO Sqsz :Size REP 4 [FD :Size RT 90] END To get this procedure to work you will have to give the variable Size a value. We do this when we call the procedure Sqsz by entering: CS Sqsz 200 This puts the value 200 into the variable Size and then draws a square of size 200. Try the following: CS MAKE "Size 10 REP 20 [Sqsz :Size MAKE "Size :Size+20] Pretty isn't it? The Logo Commands PR is the command to print. It is introduced first of all because it is used in so many of the following examples. It can be entered in its full form as PRINT. ABS As in PR ABS -3 gives the absolute value of the input number. In this case it will output 3. AND As in PR AND 3<4 7>4 prints TRUE if both conditions are true. ARC As in ARC 0 0 100 180 270 draws an arc at position 0,0 of radius 100 units from heading 180 to 270. If negative numbers are use for the start and finish then the arc is drawn as a slice of pie. eg ARC 0 0 100 -180 -270 ASCII As in PR ASCII "A prints the ASCII value of the first letter. In this case it will be 65. ATN As in PR ATN 2 outputs the arctangent (inverse of tangent) in degrees. In this case it prints the angle that has a tangent of 2. BACK or BK As in BACK 100. Moves the Turtle back 100 units. BYE Leaves the current session of Logo. CHAR As in PR CHAR 82 prints the letter corresponding to ASCII code 82. CIRCLE As in CIRCLE 0 0 100 draws a circle of radius 100 and centre at 0,0 -the centre of the screen. It does not move the Turtle. eg MAKE "R 10 REPEAT 20[CIRCLE :r*~1 :r*~1 :r MAKE "r :r+10] Note that unary negative is ~ not - as in ~2 for minus 2. CLEAN Erases the contents of the viewport but without affecting the Turtle. COS As in PR COS 20 outputs the cosine of the angle (which is entered in degrees). CS This is short for clear screen. It erases the contents of the viewport and places the Turtle at 0,0 and on a heading of 0. CT This is short for clear text. Erases the contents of the text window and places the cursor in the top left hand corner. DEGREES As in PR DEGREES 25 prints out the number of degrees in the entered number of radians. DIR As in DIR outputs all the files with a .LOG suffix in the current drive and directory. DOT As in DOT 50 50 which places a dot at 50,50 without moving the Turtle. PE followed by DOT will erase a point. EDALL Loads all the procedures and variables in the workspace into the text editor. To leave the editor use the ESCape key. EDIT or ED As in ED "Pat loads the specified procedure into the text editor. END Indicates the end of a procedure. ERALL Erases all the procedures and variables from the workspace. FENCE Limits the Turtle to the screen. It also warns you if the Turtle is out of bounds. FILL As in FILL 3. Fills the area around the Turtle with colour 3. FORWARD or FD As in FORWARD 100 moves the Turtle forward by 100 units. HEADING As in PR HEADING prints out the Turtle's heading. HOME Returns the Turtle to the Home position of 0,0 and with heading 0(North). HT This is short for hide Turtle. It makes the Turtle invisible and speeds up drawing. IF As in IF :A>:B [PR [:A is bigger]] [PR [:A is not bigger]] If the condition is true the first command is carried out. If not true the second command is carried out if it is present. The conditional statement can contain <, > or = but not combinations of them. INT As in PR INT 3.34 which prints the integer portion of 3.34 which is 3. LEFT or LT As in LT 90 which turns the Turtle 90 to the left. All angles are in degrees. LOAD As in LOAD "Mine which loads the procedures and variables in Mine into the workspace. LN As in PR LN 2 which prints the natural log of the number. MAKE As in MAKE "Side 50 which places 50 into the variable Side. This is now a global variable. The following are correct syntax: MAKE "A SIN(34) Make "A LN(34.5) Note that calculations should not contain spaces. NOT As in PR NOT(3=4) which prints True since the expression is false. OR As in PR OR (1=2) (1=1) which prints True since the one of the two conditions is true. PENDOWN or PD Puts the Turtle pen down to resume drawing after a PE or PU command. PENERASE or PE Makes the Turtle pen into an eraser by making it draw in the background colour. PENUP or PU Picks the Turtle pen up so that the Turtle can be moved without affecting the drawing. Try REP 4[ REP 10 [FD 20 PU FD 20 PD] RT 90] POS As in PR POS prints the position of the Turtle. PRINT or PR As in PR "Me prints Me. PROD As in PR PROD 2 3 or PR PROD 2 3 4 which prints the product of the numbers which follow. QUOT As in PR QUOT 24 7 which outputs the integer part of the division. In this case 3. RADIANS As in PR RADIANS 90 which will output the number of radians which was entered as degrees. RANDOM As in PR RANDOM 20 which prints out a random number between 1 and 20. REMAINDER As in PR REMAINDER 7 3 which prints out the remainder of 7 divided by 3. REPEAT or REP As in REP 4[ FD 100 RT 90] which repeats the instructions in the square brackets 4 times. RIGHT or RT As in RT 90 which turns the Turtle right by 90 degrees. ROUND As in PR ROUND 3.5 which rounds the input number to the nearest integer- in this case 4. SAVE As in SAVE "Mine which will save all the procedures and variables to the file Mine. It is possible to put a path before it to save it to a different disc or drive. SETBG As in SETBG 2 followed by CS which will then set the background to the new colour. SETH As in SETH 45 which sets the Turtle heading to 45 degrees. SETPC As in SETPC 3 which sets the pencolour to colour 3. SETPOS As in SETPOS 50 50 which puts the Turtle at co- ordinates 50,50 SETX As in SETX 100 moves the Turtle horizontally to X co-ordinate 100. SETY As in SETY 100 moves the Turtle vertically to Y co-ordinate 100. SHOWTURTLE or ST Makes the Turtle visible if it has been hidden with HT. SIN As in PR SIN 30 which outputs the sine of the angle which was input in degrees. SQRT As in PR SQRT 64 which will print out the square root of 64 being 8. SUM As in PR SUM 2 2 which will print out the sum of the numbers which follow. TAN As in PR TAN 45 which will print out the Tangent of 45 degrees. TO As in TO Sq being the first line of the procedure called Sq. TOWARDS As in PR TOWARDS 50 75 which will print the heading for the Turtle to move towards co-ordinates 50,75. WINDOW Allows the Turtle to move anywhere but if it leaves the screen area it will not be visible. WRAP Allows the Turtle to treat the screen as a sphere. When it disappears from one side it will reappear on the opposite side of the screen. XCOR As in PR XCOR will print the X co-ordinate of the Turtle YCOR As in PR YCOR will print the Y co-ordinate of the Turtle.