Logo Lesson 3 TBE 540 Fall 2004 Farah Fisher Prerequisites for Lesson 3 Before beginning this lesson the student must be able to Use simple Logo commands to make a shape Create and edit a procedure Use the following commands appropriately POTS SAVE LOAD Objectives for Lesson 3 After completing this lesson the student will be able to Move the turtle to any screen position Determine the turtle s screen position Explain the term variable Create procedures with variable input using MAKE and RANDOM Logo Screen Positions The position of the Logo turtle on the screen is described by two numbers a horizontal and a vertical coordinate The center of the screen is the turtle s home Its designation is 0 0 and all other coordinates are measured from there It is very much like graphing in algebra Logo Screen Positions The first of the two numbers describes the horizontal distance in turtle steps right or left of the center For example in the position 10 15 the 10 represents 10 turtle steps to the right of the center In the position 25 10 the 25 represents 25 turtle steps to the left of the center Logo Screen Positions The second of the two numbers describes the vertical distance in turtle steps above or below the center For example in the position 10 15 the 15 represents 15 turtle steps above the center In the position 25 10 the 10 represents 10 turtle steps below the center Guess the Positions Make your best guess about the positions Click to see the answers 2 1 4 3 Guess the Positions Possible screen positions depending on Logo version 100 50 2 1 150 75 4 3 0 50 25 25 Position Commands PR POS is the command used to print in the command window the current position of the turtle SETPOS number number or SETXY number number sets the position of the turtle SETX number changes only the first number SETY number changes only the second number HOME returns the turtle to 0 0 Challenge What shape do you think would result from these commands assume turtle starts at 0 0 Click to see the answer SETPOS 0 25 SETPOS 25 25 SETPOS 25 0 SETPOS 0 0 or HOME Challenge The commands make a square 0 25 0 0 25 25 25 0 Logo Variables A variable is a letter or word that represents a number that can vary thus the term variable In Logo variables often have a colon in front of the letter or word Sample Logo variables L2 WIDTH NAME X Logo Variables Variables must be assigned a value The Logo command MAKE is often used to fill up a variable For example the command below puts the number 17 into the variable called NUM notice the quote and lack of colon MAKE NUM 17 Logo Variables See if you can determine the final value of Z after the commands below NOTE means multiply means divide MAKE Z 25 MAKE Z Z 2 MAKE Z Z 10 MAKE Z Z 2 Logo Variables Z becomes 30 after several calculations MAKE Z 25 Z starts at 25 MAKE Z Z 2 Z is multiplied by 2 Z 50 MAKE Z Z 10 10 is added to Z Z 60 MAKE Z Z 2 Z is divided by 2 Z 30 Logo Variables After you define the value of a variable you can use it in Logo commands in place of any number Examples FD X RT D2 REPEAT 4 FD SIZE RT 90 RANDOM Logo variables can also be filled with random numbers The RANDOM command returns a number from 0 to a set limit Example RANDOM 10 returns a number between 0 and 9 Example 1 RANDOM 100 returns a number between 1 and 100 RANDOM Examples of MAKE with RANDOM MAKE Z RANDOM 15 MAKE H23 1 RANDOM 10 Z becomes a number between 0 and 14 H23 becomes a number between 1 and 10 MAKE LENGTH 10 RANDOM 50 LENGTH becomes a number between 10 and 59 10 0 to 10 49 Samples of Procedures with Variables MAKE RANDOM A variable size SQUARE TO SQUARE MAKE SIZE 10 RANDOM 100 REPEAT 4 FD SIZE RT 90 END Samples of Procedures with Variables MAKE RANDOM A variable size TRIANGLE TO TRIANGLE MAKE SIZE 25 RANDOM 50 REPEAT 3 FD SIZE RT 120 END Samples of Procedures with Variables MAKE RANDOM A variable size RECTANGLE TO RECTANGLE MAKE S1 25 RANDOM 50 MAKE S2 25 RANDOM 100 REPEAT 2 FD S1 RT 90 FD S2 RT 90 END Another Way to Fill a Variable You can also fill up a variable by defining it when you run a procedure Look at this procedure TO SQUARE S REPEAT 4 FD S RT 90 END Somehow the S needs a value Another Way to Fill a Variable To start this procedure TO SQUARE S REPEAT 4 FD S RT 90 END you would type SQUARE 50 or SQUARE 100 or SQUARE 87 The number you type after the procedure name fills the variable Another Way to Fill a Variable Another example TO TRIANGLE F REPEAT 3 FD F RT 120 END To draw a triangle with sides of 50 type TRIANGLE 50 to start the procedure Another Way to Fill a Variable Consider this example TO RECTANGLE L W REPEAT 2 FD L RT 90 FD W RT 90 END You would need two numbers after the name of the procedure the first becomes L and the second becomes W RECTANGLE 50 100 RECTANGLE 40 40 Self Check Lesson 3 In the screen below what is the best estimate of the turtle s position 50 50 50 50 50 50 50 50 Self Check Lesson 3 In the screen below what is the best estimate of the turtle s position 50 50 50 50 50 50 50 50 50 50 Self Check Lesson 3 Which of the following could not be the name of a Logo variable Z The Size SIZE B123 Self Check Lesson 3 Which of the following could not be the name of a Logo variable Z The Size SIZE B123 no spaces allowed Self Check Lesson 3 What will be the value of BIG after the Logo commands below MAKE BIG 5 MAKE BIG BIG 25 MAKE BIG BIG 7 Self Check Lesson 3 What will be the value of BIG after the Logo commands below MAKE BIG 5 BIG 5 MAKE BIG BIG 25 BIG 30 MAKE BIG BIG 7 BIG 23 Self Check Lesson 3 Suppose you want a randomly chosen number between 1 and 10 Which of the following would generate that number RANDOM 10 RANDOM 1 10 RANDOM 10 1 Self Check Lesson 3 Suppose you want a randomly chosen number between 1 and 10 Which of the following would generate that number RANDOM 10 RANDOM 1 10 RANDOM 10 1 0 TO 9 10 0 TO 10 999 Self Check Lesson 3 Suppose you have entered the procedure below What would you type to use it to draw a SQUARE with sides of 50 TO SQUARE X REPEAT 4 FD X …