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4. Procedures > Some of the Procedures in LOGO 4.1. PROCEDURES | A Logo Procedure | Writing A Procedure | Running A Procedure | Variables | Examples | 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.
4.1.2. Writing A Procedure A procedure is started by giving the TO command followed by the name of the 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 Let us write a procedure for drawing a CIRCLE:
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. 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:
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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