9. BASIC programming: Control and Repetition

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1 Am: In ths lesson, you wll learn: H. 9. BASIC programmng: Control and Repetton Scenaro: Moz s showng how some nterestng patterns can be generated usng math. Jyot [after seeng the nterestng graphcs]: Usng a repettve mathematcal sequence, we can easly draw very nterestng patterns. Moz: Yes. Generate nterestng numbers usng mathematcal calculatons and use these to generate nterestng graphcs. Execute the program step by step and understand how a sequence starts, s repeated and ends, wth for statement. clg for = 1 to 20 square=* Prnt square color blue rect square,square,, next Text output Graphcs output square square square square 16 square 25 square 36 square 49 square 64 square 81 square 100 so on untl >10 Tejas: Frst the graphcs output screen and the text output screen are cleared. Jyot: s assgned the value 1 at the start of the repetton. [ = 1] Tejas: The sequence to be repeated starts. Square of s calculated and assgned to square. Then square s prnted n text output area. [ square = 1] Jyot: square s used for x and y coordnates n the rectangle statement. The length and breadth of the rectangle s set to. A rectangle s output n the graphcs output area. Rect 1,1,1,1 Tejas: Next s ncremented by 1. The sequence s repeated tll = 20. When >20 the repetton stops. [ = 2... =20] Moz: Very good. You have explaned the repetton sequence very well. Jyot: Instead of ncrementng the value of by 1 s t possble to ncrement by more than one? 90

2 Moz: Yes. You can. For example you can wrte the repetton statement as follows: # more.kbs clg for t = 1 to 300 step 3 color red lne 0,0,300,t color blue lne 0,0,t,300 next t Graphcs output Tejas: Wow. What a pattern. Moz: Change the step to 100 and see what wll be the effect. Jyot: When the step s ncremented by 100, the sequence s repeated 3 tmes. 3 lnes of blue and 3 lnes of red are drawn. Moz: Yes. Instead of ncrementng by 1, the repetton count s ncremented by the step. Info Repetton of a block of statements - For statement Syntax for varable = expr1 to expr2 statement(s) next varable for varable = expr1 to expr2 step expr3 statement(s) next varable For statement, executes a specfed block of code a specfed number of tmes, and keeps track of the value of the varable. At the start of executon of for loop, varable s assgned the value of expr1 and the specfed block s executed. f step s not specfed, varable wll be ncremented by 1 for the second and subsequent repetton of the specfed block. If step s specfed, varable wll be ncremented by expr3 for the second and subsequent repetton of the specfed block. for = 20 to 25 step 5 Prnt + square = + * next for = 20 to 25 Prnt + square = + * next for = 20 step -1 Prnt + square = + * next For loop termnates when the value of varable exceeds expr2. Tejas: Usng the lne statement nterestng graphcs have been generated. Moz: Rght. Look at the lnes closely n the output of the program more.kbs. Jyot: They look crooked. The computer s not able to draw straght lnes. The pattern looks lke the prnt on our table cloth at home. 91 Insde the for loop: t 1... next t t 4 (Step command ncrements the value of t by... 3)... next t... so on untl t becomes greater than square = square = square = square = square = square = square = square = square = square = square = square = square = square = 400 Moz: You are rght. These patterns are used n textles. The nterestng graphc s generated because of the computer beng unable to draw perfectly straght lnes. It approxmates a straght lne by drawng the pxels n a star step fashon. Such patterns generated wth lnes are called a more pattern.

3 clg lne 0,0,1,255 lne 255,255,1,0 lne 1,255,255,255 Grapc output Graphcs Drawng a lne: lne statement Info Syntax lne start_x, start_y, fnsh_x, fnsh_y Draw a lne one pxel wde from the startng pont to the endng pont, usng the current color. (start x, start y) (fnsh x, fnsh y) Jyot: In Scratch we could execute a block usng a condton. I want to wrte a program usng the Proft and Loss flowchart. What s the syntax of If statement n Basc? Decsons Executon branchng If statement Info Syntax f condton then statement(s) end f f condton then statement(s) else statement(s) end f The f statement allows you to control f a program executes a secton of code or not, based on whether a gven condton s true or false. The condton whch s also referred to as boolean condton can contan comparson operators or logcal operators. (A table of the operators s gven separately). The evaluaton of the condton s ether true or false. At the start of the executon of f statement the condton s evaluated. ooif the condton s true the block of statements followng then are executed. ooif the condton s false, the executon contnues ether n the else block (whch s usually optonal), or f there s no else branch, then the executon contnues after the end f. It s often customary to ndent the statements wthn the f or else block. cls nput What s your age, myage nput What s your frend s age?, frendage f myage = frendage then Prnt You and your frend of same age endf What s your age 13 What s your frend s age? 14 Frst Number 35 Second number 90 Computerj: Yes Tejas: The flowchart does not show what should be done f both CP and SP are equal. Let us use the else n f statement to take care of ths condton. Moz: Good. You must take care of all the condtons that are possble. 92

4 Jyot: We can use comparson operators to compare CP and SP and fnd f t s proft, loss or the values are equal. Comparson Operators In a program we often need to compare two values n a program to decde what to do. A comparson operator (ex: <, >, <=) works wth two values and returns true or false based on the result of the comparson. Comparatve operators Descrpton Example expr1 < expr2 Evaluates to True f value of expr1 s less than value of expr2, 2<4 s True else to False. expr1 > expr2 Evaluates to True f value of expr1 s greater than value of expr2, (2+5)>(3+4) s else to False. False expr1 = expr2 expr1 >= expr2 expr1 <= expr2 expr1 <> expr2 Evaluates to True f value of expr1 s equal to value of expr2 else to False. Evaluates to True f value of expr1 s greater than or equal to value of expr2, else to False. Evaluates to True f value of expr1 s less than or equal to value of expr2, else to False. Evaluates to True f value of expr1 s not equal to value of expr2 else to False. 298=298 s True 2>=4 s False 2<=4 s True 2<>4 s True Jyot: Let us see f we can dsplay an mage n the graphcs output area. I have drawn mages for proft and loss. Tejas: We can use mgload. Ths s very easy we have to just provde x,y coordnates where we want the mage dsplayed and the mage fle name. Let us also check how to dsplay a capton for the mage n graphcs area. Jyot: Dsplayng text also has smlar syntax to mgload. In place of fle name we have to provde the text n quotes. Graphcs Loadng an mage mgload statement Info Syntax mgload x, y, flename mgload x, y, scale, flename mgload x, y, scale, rotaton, flename Imgload reads the mage n the Grapc output fle specfed n the flename and dsplays t on the graphcs output area. The x, y coordnates specfy the locaton of the center of the mage, where the mage should be dsplayed n the graphcs output area. Grapc output Many of the mage fle formats are recognzed by the program. Some of these formats are bmp, png, gf, jpg and jpeg. Scalng and rotaton s optonal. o oscalng s used to resze the mage. Note that scale Grapc output s specfed by the decmal scale where 1 s full sze. oothe mage can be rotated around t s center by specfyng how far to rotate by specfyng the angle (0 to 360). 93

5 The program wrtten by Tejas and Jyot. Note we have to modfy the flowchart to nclude = condton also. Wll also modfy program later. Flowchart: How to fnd proft or loss Start Read Cost prce (CP) Read Sellng prce (SP) Is SP=CP Yes Prnt no proft or loss No Is SP>CP Yes Proft= SP-CP No Loss= CP-SP Prnt Proft Prnt Loss Stop Text output Graphcs output PROFIT CP SP Proft Text output CP 567 SP 500 Loss 67 Graphcs output LOSS 94

6 Jyot: I have a lst of words. I want to use these to wrte a quz program. Let us fnd how to save these words and later on use them to prepare a quz. Tejas: We can defne a lst whch s called an array as follows. Dm array_name(ndex) Dm array_name$(ndex) Snce our lst wll contan strng values we have to add $ at the end of the array name smlar to a strng varable. We have to also specfy the number of values the lst wll contan n the brackets. Jyot: The computer then has to reserve 5 memory locatons for the array. What s the name gven to each locaton? Moz: The computer names the 5 memory locatons as adjectv$(0), adjectv$(1), adjectv$(2), adjectv$(3), adjectv$(4). The number n the brackets s called an ndex. Ths s also called the numerc address of the tem n a lst or an array. Tejas: Ths s smlar to one column n a spreadsheet. Moz: Yes. Note that ndex starts wth 0, nstead of 1. Each tem of an array s called the element of the array. The dm statement assgns an empty strng to each element n the array. Ths s also called ntalzng the array wth a value. Jyot: If t s a numerc array then what s the ntalzaton value? Moz: Each element of a numerc array s ntalzed wth the value 0. dm adjectv$(5) adjectv$(0) adjectv$(1) adjectv$(2) adjectv$(3) adjectv$(4) Jyot: Let us now assgn values to the lst. adjectv$ = { Amazng, Slppery, large, Monthly, Jucy } Tejas: Now let us retreve the values and prnt them. adjectv$(0) Amazng adjectv$(1) Slppery adjectv$(2) large adjectv$(3) Monthly adjectv$(4) Jucy Dm adjectv$ (5) adjectv$ = { Amazng, Slppery, large, Monthly, Jucy } prnt Adjectves prnt for = 0 to 4 Prnt adjectv$[] next Adjectves Amazng Slppery large Monthly Jucy 95

7 Creatng a one dmensonal array Dm (Index) Info Syntax to create a one dmensonal array Dm array_name(ndex) Dm array_name$(ndex) Dm statement creates an array n the computer s memory wth the varable name provded n the array_ name. Arrays can be ether numerc or strng. Syntax of namng of the array follows the same syntax as numerc and strng varable name. The number of tems n an array s specfed by the ndex, whch s always an nteger value greater than 1, n the parenthess. The dm statement ntalzes each element n the new array wth ether zero (0) f the array s a numerc array or empty strng ( ), f the array s a strng array. Syntax to assgn and to retreve values of an array array_name = {value1,value2,value3,...} array_name$={ strng1, strng2,...} array_name[ndex] = value array_name$ [ ndex] = value Each element of an array can also be assgned a value. Array elements are assgned by smply usng the element ndex n square brackets along wth the array name. dm marks (2) dm name$ (3) Dm marks (3) marks = {90,86,65} Dm marks (3) marks = {90,86,65} Total = marks[0]+marks[1]+marks[2] prnt Total marks= + Total Dm a(3) a[0]= 89 a[1] = 23 prnt a[0] + a[1] Total marks= marks 0 marks1 0 names$ marks0 90 marks1 86 marks2 65 Tejas: Wow. Ths s good. We want to convert the game Guess my number nto a program. In ths game the computer chooses a number. The user has to keep guessng the number, tll the guess s correct. Jyot: Is there some way to make the computer choose a random number? Moz: Yes. Check out the Functons secton n the Basc-256 manual. Jyot: Yes, there s a functon rand. It s exactly what we want. number = rand *50 prnt number Number

8 Tejas: The functon rand gves a decmal number. We want a whole number. Moz: Snce you want the user to guess a number from 1 to 50 multply the number generated by rand wth the last number n your range whch s 50. Then convert the number you get to nteger usng the nt functon. Jyot: Oh! Got t. For example: x = rand =.902 x = rand * 50 =.902 * 50 = x = nt(rand * 50) = nt(.902 * 50) = nt(45.100) = 45 Moz: Rght. When you use max of the range you get numbers wthn the range. You can experment and fnd out how ths works wth varous numbers. Now go ahead and wrte your program. number = nt (rand *50) prnt number 22 Functons Generatng a random number Info Syntax rand The functon rand returns a random number. Rand can be used n an expresson or assgned to a varable. The random number generated vares from zero to 1. rand can be used n an expresson. number = rand rand_nt = nt (rand) nt_1to50 = nt (rand*50) prnt rand = + number prnt rand_nt = + rand_nt prnt rand_1to50 = + nt_1to50 rand = rand_nt = 0 rand_1to50 = 44 Jyot: Oh! So we have to use nt to convert the decmal number to nteger. Tejas: I just can t wat to wrte the game. Let us start. Moz: Frst wrte the man steps of the program. Then convert t nto a BASIC program. Remember to put comments n the program. 1. Declare and ntalze array to dsplay chance count. 2. Generate a random number between 1 and 50 store t n mynumber. 3. Ask the player to gve the range for hs/her guess. 4. Take the player s nput. 5. Compare and reply f mynumber s wthn the range. 6. Ask player to now guess the number. 7. Player guesses number. 8. Compare and dsplay smley and a msg f the guess s equal to mynumber. 9. Compare and dsplay approprate msg f the guess s greater than or less to mynumber. 10. After 5 chances dsplay mynumber wth approprate messages. 97

9 5. Fnal program Guess the number that computer thnks of: Verson 3 #Guess my number cls clg #Declare and ntalze array to dsplay chance count dm chance$(6) #Intalze Y-coordnate, chance strngs n array, specfy font for graphc dsplay Y= 5 font Tahoma, 12, 50 chance$ = { NIL, Frst, Second, Thrd, Fourth, Ffth } #Generate a random number between 1 and 50 mynumber = nt(rand *50 + 1) prnt I thnk of a number between 1 and 50. Guess my number! prnt prnt Here are 3 chances where you get some hnt about my number! For =1 to 3 #Dsplay chance count n graphcs output color blue Y = Y + 25 text 0, Y, chance$[] + Chance Prnt #Player gves the range n whch he/she thnks the number s Prnt Player asks: Is Your number between nput Frst number, frstnumber nput Second number, secondnumber #Compare and reply f mynumber s wthn the range f (mynumber >= frstnumber) and (mynumber <= secondnumber) then Prnt Computer reples: Yes else Prnt Computer reples: No endf Y= Y + 25 Next #Player guesses number for = 1 to 3 nput Computer: Guess my number, yourguess #Compare and dsplay msg f the guess s not equal to mynumber f mynumber > yourguess then prnt My number s greater than your guess. endf f mynumber < yourguess then prnt My number s less than your guess. endf f mynumber = yourguess then prnt You guessed my number wth + + chances. Well done. end endf next #After 5 chances dsplay mynumber Prnt My number s + mynumber font Tahoma,20,75 text 5,125, Better luck next tme I thnk of a number between 1 and 50. Guess my number! Here are 3 chances where you get some hnt about my number! Player asks: Is Your number between Frst number 1 Second number 25 Computer reples: Yes Player asks: Is Your number between Frst number 2 Second number 12 Computer reples: No Player asks: Is Your number between Frst number 13 Second number 20 Computer reples: Yes Computer: Guess my number 16 My number s less than your guess. Computer: Guess my number 15 My number s less than your guess. Computer: Guess my number 14 My number s less than your guess. Computer: Guess my number 13 You guessed my number wth 3 chances. Well done. Y Chance$ [1] Chance$ [2] Chance$ [3] Chance$ [4] Chance$ [5] Chance$ [6] mynumber Frst number Second number Y Frst number Second number Y Frst number Second number Y Your guess Your guess Your guess Your guess 5 NIL Frst Second Thrd Fourth Ffth

10 #Reuse the graphc code from CM VI to dsplay smley clg color yellow rect 0,0,300,300 # draw the face color whte crcle 150,150,100 # draw the mouth color black crcle 150,160,70 # A whte crcle s supermposed on the black crcle to draw the mouth color whte crcle 150,150,70 # put on the eyes color black crcle 105,110,15 crcle 185,110,15 #End of reuse code Graphc output Wake up! Bos Boot up! I am ready! Lesson Outcome At the end of the lesson, you wll be able to: Categorze a computer component nto hardware and software. Identfy varous parts nsde the computer and state ther functons. Os 99

11 Level VII Lesson 9 WORKSHEETS 1. a. b. What s the output of the program? for t = 1 to 10 step 2 p=3 prnt p*t ; next t Multplcaton table of 3. 3, 9, 15, 21, 27 v. Multplcaton table of 2 Sum=245 If Sum>245 then Prnt You reached level 3 else Prnt Stll to go End f. You reached level Stll to go v. none of the above c. for t = 1 to 10 for p=1 to 10 prnt p*t next p next t. Squares of numbers from 1 to 10. Multplcaton tables of all numbers from 1 to 10. Squareroots of numbers from 1 to 10 v. None of the above d. Dm Workngdays$(4) Workngdays$={ Monday, Tuesday, Wednesday, Thursday, Frday } Prnt Workngdays$[2]. Monday. Tuesday. Wednesday v. Thursday e. Dm a(3) a[0]= 89 a[1] = 23 a[2] = a[0] + a[1] For = 1 to 2 Prnt a[]; next v

12 Level VII Lesson 9 WORKSHEETS f. Number = rand*100 Prnt Number... v. Any number between 0 and 100 Any number from 0(ncludng 0) to 100( excludng 100) Any number from 0(ncludng 0) to 100( ncludng 100) Any number from 0(excludng 0) to 100( ncludng 100) 2. Here s a program wrtten n Basc-256. Insert the necessary comments clearly statng the functon of each code segment. # Dm Answer$(5) Dm Dsplay(5) Answer$ = { Frst, Second, Thrd, Fourth, Ffth } # For =0 to 4 Input Answer$[] + Number:, answer Dsplay[] = answer Next # For t=0 to 4 Prnt Dsplay[t] Next t 3. Insert the rect statement n the followng program that would gve the output shown n red n the graphcs output area. clg for = 1 to 20 square=* Prnt * color blue rect square,square,, color red Graphcs output next 101

13 Level VII Lesson 9 WORKSHEETS 4. a. Here s a program to fnd the number of people who own a car n a buldng. The number of resdents n the buldng s 6. Go through the program and see whether the sequence s correct. If there s a mstake correct t and verfy by runnng t n Basc-256. For =0 to 5 counter=0 Prnt Do you own a car? (answer wth yes or no) Input answer$ If answer$= yes then counter=counter+1 end f Next prnt Number of resdents wth a car: + counter b. Now nsert the code fragment to record the answers of each resdents n the buldng. Hnt: Use an array to store the answers of the resdents. 102

14 Level VII Lesson 9 WORKSHEETS 5. a. Use the followng graph sheet to draw the followng shapes. rght trangle pentagon star b. Wrte a program n Basc-256 to draw any one of the above shapes usng the lne statement. 103

15 ACTIVITY Level VII Lesson 9 1. Here s a program whch uses For loop. Check what s the output you wll get when you ntroduce Step whle ncrementng the value of. cls clg For = 1 to 20 square=* prnt + and + square rect square,square,, next Check the out output when the steps are 2.5 and Suppose your class has 45 students. Wrte a program to fnd the number of students present today what s the number of students absent? Hnt: Use For loop, If then else and counters to complete the program. Expl re 1. How to add comments n a document. 2. How to record changes made n a document. 3. Calculate word count for selected text. 104

16 Teacher s Corner Book Level VII Lesson 6 105