Green-Computer-Book-8

GREEN Computer Book-8 251 Press Esc key to clear the welcome dialog box or Click on the area with the message to clear the screen. Press Alt + Enter to enlarge the QBASIC window to fit in the screen. Parts of QBASIC Windows QBASIC Editor Screen consists of four main parts. They are Menu Bar, View Window, Immediate Window and Reference Bar. 1. Menu Bar: Menu Bar provides pull down menus and their options to work with QBASIC easily. 2. View Window: We write and edit programs in View Window. It is the largest part of the QBASIC Editor Screen. 3. Immediate Window: You can type and test a functioning of statement in this window by pressing Enter key after a line of statement. 4. Reference Bar: It displays the information about the active keys of the QBASIC Editor as SHIFT +F1, F2, F5 and F8. Writing New Program 1. Click on File menu or press ALT + F. 2. Select New Program option.

252 GREEN Computer Book-8 A blank screen with blinking cursor appears. Now, you can type your program. Saving a Program 1. Click on File menu or press ALT + F. 2. Select Save or Save As option. A dialog box appears. 3. Specify the desired drive location and folder where you want to save the file. (Example: E:\Class 8)

GREEN Computer Book-8 253 4. Type the filename in File Name box. 5. Click on OK or Press Enter key. Running Program 1. Click on Run menu or Press ALT +R. 2. Select Start option. Or Press F5 key to continue execution from previous point or SHIFT + F5 key to execute from the beginning. You can press any key to return to the QBASIC Editor Screen. Opening an Existing File 1. Click File menu or Press ALT + F. 2. Select Open option. A dialog box appears 3. Choose the filename from the location where the file is saved. 4. Select the filename. 5. Click on OK or Press Enter key. Cut and Paste 1. Highlight the line of statement or block of statement to be moved. 2. Click on Edit menu and select Cut. Or Press Shift + Del key to cut. 3. Go to the desired location

254 GREEN Computer Book-8 4. Click on the Edit menu, Select Paste. Or Press Shift + Insert key for paste. Exiting from QBASIC 1. Click on File menu or Press ALT + F. 2. Select Exit option. Characters Set in QBASIC One of the virtues of BASIC language is a simple way in which data is represented. Data, in a basic program, may be of two types. These are number or numeric data and a set of characters called string or literal data. Type Character or Symbol Alphabet A to Z or a to z Digits 0 to 9 Operators +, -, *, /, \, MOD, ^, ( ), =, <, >, >=, <=, <> Special Characters $, #, !, %, & Constants and Variables Constants Constants are the data or values that do not change when the program executes. The data types accepted by QBASIC can be termed as Constants. There are two types of Constants in QBASIC. 1. Numeric Constant 2. String Constant 1. Numeric Constant A number or a set of numbers used in mathematical calculations and comparisons is known as Numeric Constant. It is the general type of number and appears normal like we write in English or mathematics. It should be stored in Numeric Variable.

GREEN Computer Book-8 255 Valid Numeric Constant 1000 -253 1056.50 -25.64 Numeric Constant can be positive or negative numbers with decimal values. Invalid Numeric Constant a. 10,00 Comma is not acceptable. b. 100% No sign is accepted. c. 1 23 Space is not allowed. 2. String Constant A set of alphanumeric values and special characters is known as String Constant. Normally, it is enclosed within double quotation marks. It should be stored in String Variable. Valid String Constant Invalid a. “Kathmandu” Kathmandu” b. “Programming is fun” “programming” “is” “fun” c. “---------special characters can be used -------” I love Nepal d. “5526783” 984150 Variables Variable is the name or an entity of space in the memory location that can hold alphanumeric and numeric values. A variable can contain a number, a special character, a word, a sentence or an entire paragraph as its value. The value of variable can change during the program execution. It is further divided into two categories on the basis of data it stores. 1. String Variable 2. Numeric Variable 1. String Variable It is the data entity that holds alphanumeric values. The name of string variable ends with dollar ($) sign. It also accepts number as its value but the number does not take part in mathematical calculations. The value of String Variable is the string constant.

256 GREEN Computer Book-8 Valid String Variable a. N$ b. FirstName$ c. Address$ d. pH$ e. R15$ Invalid String Variable a. 1N$ Variable name doesn’t start with a number. b. First Name$ Space is not allowed. c. Address $ sign is missing. 2. Numeric Variable It holds number for mathematical calculations. It cannot accept text as its value. Numeric Variable is further divided into four types. Data type Declaration Maximum Minimum Bytes used Integers % 32,767 -32,768 2 Long Integers & 2,147,483,647 -2,147,483,648 4 Single (7-digit) Precision ! 3.402823 +38 1.401298 E-45 4 Double (16-digit) Precision # 1 . 7 9 7 6 9 3 1 D+308 4.940656 D-324 8 String $ 32767 0 2 Rules for naming Variable a. First letter of a variable name must be an alphabet. b. Variable name can be up to 40 characters long. c. Variable name can be in UPPERCASE, lowercase or a combination of both. d. Space in between the variable name is not allowed. e. Variable name should be precise and meaningful. f. Some reserved words such as SQR, PRINT, LEN, etc. cannot be used as variable name g. Letters (a to z an A to Z) and numbers (0 to 9) can be combined to write variable name.

GREEN Computer Book-8 257 Operators and Expressions Operators are signs or symbols that perform mathematical and logical operation such as addition, multiplication, comparisons, assign values and make logical decisions. The types of operators are: a. Arithmetic Operators b. Relational Operators c. Logical Operators d. String Operators e. Assignment Operators a. Arithmetic Operators They perform mathematical calculations like addition, subtraction, multiplication, division, etc. They give numeric values (numbers) as a result. Arithmetic Operators Function Example ^ (Exponentiation) calculates exponent (Power of the number) 2^3=8 * (Asterisk) multiplies the numbers 2*3=6 / (Forward slash) divides the number 5/2=2.5 \ (Backward slash) performs division and gives only integer number as quotient 5\2=2 MOD calculates remainder 5 MOD 2=1 + performs addition 3+1=4 - performs subtraction 3-1=2 b. Relational Operators (=, <, >, >=, <=, <>) They compare the values and give result as True or False. They are used to make decisions in the program. If a= 5, b= 8 then; = is equal to a=b = false > is greater than a>b = false < is less than a<b = true > = is greater than or is equal to a>= b =false < = is less than or is equal to a<=b = true <> is not equal to a<>b true

258 GREEN Computer Book-8 c. Logical Operators (AND, OR ,NOT) They help to make decisions as True or False. It combines multiple conditions to make a complex logic. Truth Table A truth table shows the outputs obtained from a logic circuit or gate as consequences of specific inputs. Truth Table for OR operator Condition1 (x) Condition2 (y) Output z= (x OR y) False(0) False(0) False(0) True(1) False(0) True(1) False(0) True(1) True(1) True(1) True(1) True(1) Let a=10, b= 15, c= 20 Condition 1 (x) Condition 2 (y) Output (x OR y) a>b= false a>c=false False OR False = False a>b= false a<b= true False OR True=True a<b=true a>b= false True OR False=True a<b=true a<c= true True OR True= True Truth Table of AND operator Condition1 (x) Condition2 (y) Output z= (x AND y) False(0) False(0) False(0) True(1) False(0) False (0) False(0) True(1) False (0) True(1) True(1) True(1)

GREEN Computer Book-8 259 Let a=10, b= 15, c= 20 Condition 1 (x) Condition 2 (y) Output (x OR y) a>b= false a>c=false False AND False = False a>b= false a<b= true False AND True=False a<b=true a>b= false True AND False=False a<b=true a<c= true True AND True= True Truth Table of NOT Input Output False(0) True (1) True(1) False(0) d. String Operator It combines text with the " + " sign. This process is known as concatenation. Example: A$="Program" B$="ming" Print A$+B$ It will result in Programming. Operands Operands are constant values or variables on which mathematical or logical operations take place. Let us look at the example below: X = 5 + 10 Sum = A + B In the above two expressions, the numbers 5, 10 and the variables A and B are called the operands. The plus is the arithmetic operator which is working on the operands.

260 GREEN Computer Book-8 Expressions The combination of operators, variables and constants is known as an expression. The variables or constants used before or after an operator are known as operand. An expression gives out a value as a result. Conversion of Algebraic Expression into QBASIC Expression Algebraic Expression QBASIC Expression a. h2 = p2 + b2 h^2 = p^2 + b^2 b. (a2 – b2 )=(a +b) (a –b) (a^2+b^2) = (a + b) * (a – b) c. V = L3 V = L^3 d. A ÷ B x C A / B * C e. average = total ÷ N average = total / N POINTS TO REMEMBER 1. QBASIC is the high level programming language. 2. Constants are the data or values that do not change when the program executes. 3. Variable is the space in the memory location that can hold alphanumeric and numeric values. 4. String variable is the data entity that holds alphanumeric values. 5. Numeric variable holds number for mathematical calculations. 6. Operators are signs or symbols that perform mathematical and logical operation such as addition, multiplication, comparisons, assign values and make logical decisions. 7. Operands are constant values or variables on which mathematical or logical operations take place. 8. The combination of operators, variables and constants is known as an expression. 9. Relational operators compare the values and give result as True or False.

GREEN Computer Book-8 261 Exercise 1. Answer the following questions. a. What is QBASIC? Write the versions of QBASIC. b. Write the features of QBASIC. c. Write steps to starting QBASIC. d. What is Immediate Window? e. Write steps for saving a program. f. Write steps to cut and paste block of codes in QBASIC program. g. Define operator. List out the types of operator. h. Make truth table of AND, OR, and NOT operators. i. What is variable? Write rules for naming variable. 2. Write the function of the following shortcut keys. • ALT + F • ALT + R • Shift + Insert • Shift + Del • F5 • SHIFT + F5 3. Fill in the blanks. a. String Variable ends with a ........................sign. b. Variable name can be up to ........................ characters long. c. A variable name should always start with an ......................... d. QBASIC was first invented by …………………………….. of Dartmouth College, U.S.A. in 1964. e. String variable is the data entity that holds …………………..values.

262 GREEN Computer Book-8 4. Evaluate and find the output of the following if a=15, b=20 and c= 5. a. (a + b +c )/4 b. (a + b +c ) \5 c. b MOD c d. b MOD a * c e. (a+b)^(1/2) f. (a+b+c)^(1/3) g. 12 MOD 4 = 3 h. 45>56 AND 45=45 i. 45>76 AND 25<>5 j. a<b OR a<>c 5. Identify the valid and invalid variables and constants: a. 2654 b. Name$ c. 0.65 d. “hi!” e. “12/7/1972” f. 20/A g. “Ktm Nepal” h. 1N i. A$ j. 9+8 j. Num k. $city l. -77 m. Roll n. sum of two numbers 6. Complete the Table if a=15, b= 5, c= 10. Condition 1 (x) Condition 2 (y) Output (x OR y) Output (x AND y) a>b= True A<c=False True OR False = True True AND False = False a>b= ? a<b= ? ? ? a<b=? a>b= ? ? ? a<b=? a<c= ? ? ? 7. Covert the following Algebraic Expressions into QBASIC Expressions: a. A = 2( L + B) b. SI = PTR/100 c. A = ½ (b x h) d. F=180/100C + 32 e. (a2 – b2 )=(a + b) (a – b) f. a2 + 2ab + b2

GREEN Computer Book-8 263 QBASIC Statements and Library Functions 21 QBASIC Statement is an instruction used in QBASIC to perform a specific task in a program. It helps to solve problems with the help of a computer. All the command words have to be written using some standard rules, which are called “Syntax Rules”. Syntax is the grammar of writing a statement in a language. Some of the statements are : Clearing the screen CLS This statement is used as the first line of every program so that the screen is cleared each time the program runs. It helps the program to start with a fresh screen. You can insert the CLS statement anywhere in a program. Syntax: CLS REM Statement This command is used to put remarks to a program or a line of statement to make the code more understandable. REM statement is used throughout the program to explain what your code is trying to accomplish. You can type (') apostrophe instead of REM statement. Syntax: REM remarks

264 GREEN Computer Book-8 LET Statement It is used to assign value to a variable. It is optional. Syntax: [LET] variable = expression LAB Practice 1 CLS REM program to find sum of two numbers LET a= 10 LET b= 15 LET sum = a+b PRINT sum END PRINT Statement It displays the value or values of variables on the screen. The variables and the values are used to the right of PRINT statement. Syntax: PRINT [prompt string];expression Where, the prompt here means the message you keep enclosed within the double quotation marks. Generally, it is a string constant defining the type of input in the variable. LAB Practice 2 CLS REM program to print your name LET Name$= “Isha” PRINT “My name is”;Name$ END

GREEN Computer Book-8 265 LAB Practice 3 REM program demonstrating print statement CLS INPUT “Enter a name of student :”; N$ INPUT “Enter marks in English”; Eng INPUT “Enter marks in Nepali”; Nep INPUT “Enter marks in Science”; Sci INPUT “Enter marks in Computer”; Comp Total = Eng+Nep+Sci+Comp PRINT “The student is”; N$ PRINT “Marks in English is”; Eng PRINT “Marks in Nepali is”;Nep PRINT “Marks in Science is”;Sci PRINT “Marks in Computer is”;Comp PRINT “The total score in four subjects is”; Total END The above program will get executed as described below: Enter a name of student? Bikram Enter marks in English? 80 Enter marks in Nepali? 82 Enter marks in Science? 85 Enter marks in Computer? 90 The student is : Bikram Marks in English is 80 Marks in Nepali is 82

266 GREEN Computer Book-8 Marks in Science is 72 Marks in Computer is 90 The total score in four subjects is 337 READ.....DATA statement READ statement accepts data to a variable which are stored in DATA statement. More than one variable name can be used with READ statement. DATA statement supplies data to the variables in READ statement. Syntax: READ variable list DATA value list Example: READ Name$, Add$, salary DATA Shanvi, Sanepa, 5000 In this example, the variable Name$ will read the data Shanvi from DATA statement. Likewise, Add$ and salary will read the data Sanepa and 5000 from the DATA statement respectively. LAB Practice 4 Type the following codes in QBASIC screen and run the program. REM PROGRAM USING READ DATA STATEMENT CLS READ Name$, Add$, salary DATA Shanvi, Sanepa, 5000 PRINT Name$, Add$, salary END Note: Run the program by pressing F5 or Shift + F5. LAB Practice 5 REM to find area of circle using READ – DATA statement CONST PI = 3.1416

GREEN Computer Book-8 267 READ r LET a = PI * r^2 PRINT “Area of circle:”; a DATA 5 END END Statement END statement is used to end the program. It assures you that the program is complete. INPUT Statement INPUT statement allows a user to enter values to variable during program execution. This is the most commonly used statement for entering the values. Syntax: INPUT [;] [prompt string] [;][,] variable, [variable, ....] Understanding Syntax INPUT Keyword in capital represents BASIC statement. [;] It causes the cursor to remain in the same line after the user presses Enter key. Prompt string It displays a prompt to input. The string must be enclosed within double quotes. [;] It prints a question mark (?) at the end of the prompt string. Variable It denotes a valid variable name to be used. [Variable, ...] It denotes other variable names that can be typed separated by a comma (,). CONST statement Purpose: Declares one or more symbolic constants. Syntax: CONST constantname = expression [,constantname = expression]...

268 GREEN Computer Book-8 LAB Practice 6 CLS LET R= 5 CONST PI = 3.141593 PRINT "Area = "; PI * R ^ 2 END Conditional Branching Statement This type of statement is executed only when a given condition is satisfied. For example: IF…THEN…ELSE statements. IF...THEN…ELSE Statement It is used to make comparison between two or more values. The statement is also used while making decisions. Syntax: IF condition THEN (block of statement1 to be executed) ELSE (block of statement2 to be executed) END IF The condition following the IF statement is processed first. If the condition is true, statements which appear after THEN statement will be processed. If the condition is not true, then the ELSE statement will be executed. LAB Practice 7 REM program to enter a number and check it is less than 10 or not CLS INPUT "Enter a number: "; N IF N < 10 THEN

GREEN Computer Book-8 269 PRINT "It is less than ten";N ELSE PRINT "it is more than ten";N END IF END LAB Practice 8 REM program to enter any two numbers and check find the greater one CLS INPUT "Enter first number: "; N1 INPUT "Enter second number: "; N2 IF N1> N2 THEN PRINT "the first number is greater";N1 ELSE PRINT "the second number is greater";N2 END IF END IF...…ELSE/IF……END/IF Statement These blocks of statements allow you to have more than one IF…THEN statements in the same program. Syntax: IF condition1 THEN statement block1 ELSEIF condition2 THEN statement block 2 ELSEIF condition 3 More to know When the program encounters the IF statement, the program tests the first condition1. If the first condition1 becomes true, the program executes the firs statement block1. If condition1 is false then it checks condition2….. if all conditions are false then it executes the statement block after ELSE.

270 GREEN Computer Book-8 statement block 3 ELSE Statement block 4 END IF LAB Practice 9 REM program to enter any three numbers and find the greatest number CLS INPUT “ Enter the first number”, a INPUT “ Enter the second number”, b INPUT “ Enter the third number”, c IF a>b AND a>c THEN PRINT “ First number is greatest”;a ELSEIF b>a AND b>c THEN PRINT “ Second number is greatest”;b ELSEIF c>a AND c>b THEN PRINT “ Third number is greatest”;c ELSE PRINT “ All are equal” END IF END Statements variable Operators output CLS, INPUT IF…THEN..ELSE, PRINT, END a, b, c all are numeric variable > relational AND logical operator Third number is greatest 20 Description Table

GREEN Computer Book-8 271 Press F5 Enter the first number? 10 Enter the second number? 15 Enter the third number?20 Third number is greatest 20 LAB Practice 10 REM Program to enter any number from 1 to 7 and print the matching day CLS INPUT “Enter any number ”; Num IF Num =1 THEN PRINT “It’s Sunday” ELSEIF Num =2 THEN PRINT “It’s Monday” ELSEIF Num =3 THEN PRINT “It’s Tuesday” ELSEIF Num =4 THEN PRINT “It’s Wednesday” ELSEIF Num =5 THEN PRINT “It’s Thursday” ELSEIF Num =6 THEN PRINT “It’s Friday” ELSEIF Num =7 THEN PRINT “It’s Saturday” ELSE PRINT “Invalid number” END IF END on

272 GREEN Computer Book-8 SELECT CASE statement Select case is another conditional statement. It is almost like IF...THEN...ELSE. What if you have 5 or 6 friends that might use your computer and you want the computer to say something different to each of them? Syntax: SELECT CASE <variable> CASE <value1> (Block of statement 1 to be executed) CASE <value2> (Block of statement 2 to be executed) CASE <value3> (Block of statement 3 to be executed) . . . . . END SELECT CLS INPUT "Enter your name: ", Name$ SELECT CASE Name$ CASE "Ram" PRINT "Greetings, oh powerful master" CASE "Hari" PRINT "Go away!"

GREEN Computer Book-8 273 CASE ELSE PRINT "Hello, "; Name$; ". How are you?" END SELECT END SELECT CASE first checks Name$ for the value "Ram". If it finds it, it does the PRINT after the CASE "Ram". When the PRINT is done, it skips over the rest of the CASEs. It keeps checking against each CASE until it gets to CASE ELSE. If it hasn't found anything, it will do whatever is after the CASE ELSE. SELECT CASE can also be used with numbers as well as strings. Here's a quick example: CLS INPUT "Enter a number: ", Number SELECT CASE Number CASE 1234 PRINT "Thank you for entering the secret number 1234" CASE 22 PRINT "Well, 22 is an interesting number" CASE ELSE PRINT "You must not know the secret number" END SELECT END Library Functions Library Functions are the set of executable block of instructions capable of doing some specific tasks. They are also called built-in functions as they are ready to be used. They are programmed by the software developer and attached along with the software. Library Functions are of two types. They are String Functions and Mathematical.

274 GREEN Computer Book-8 Functions take data or variables inside the parenthesis (), i.e. bracket and is known as argument. They are used along with other QBASIC statements. Generally, the String Functions give out string data as output after processing of the data whereas Mathematical Functions give number as an output after the processing. Some of the Library Functions are: 1. UCASE$( ) This function converts the supplied string to capital letters. You can directly supply a string data enclosed within inverted comma or a string variable containing string data. This can be categorized under String Function. Syntax : UCASE$ (string/variable) Example1 : UCASE$ ("kathmandu is the capital city of nepal.") This will change the text "kathmandu is the capital city of nepal." to capital letters as "KATHMANDU IS THE CAPITAL CITY OF NEPAL." Example2 : n$="kathmandu is the capital city of nepal." UCASE$(n$) It converts the text "KATHMANDU IS THE CAPITAL CITY OF NEPAL." 2. LCASE$( ) This function changes the supplied string into lowercase characters i.e. small letter alphabet. You can directly supply a string data enclosed within inverted comma or a string variable containing string data. This is also a String Function. Syntax : LCASE$(string or variable) Example1 : LCASE$("I Love Nepal") It converts the text into lower case “i love nepal” Example2 : n$="I Love Nepal " LCASE$(n$) It converts the text into lower case “i love nepal”

GREEN Computer Book-8 275 3. LEFT$( ) This function returns specified number of characters from the left most position of a string. Syntax : LEFT$(string, number) Example1 : LEFT$("Janakpur",4) It returns 4 characters from the left of the string “Janakpur” i.e. Jana. Example2 : L$="Janakpur" LEFT$(L$,3) It returns four characters from the left of the string "Janakpur" i.e. Jan. Solved Example REM program to extract number of characters from left most position of the string CLS L$="COMPUTER" PRINT LEFT$(L$,3) END This will print three characters from left of the string COMPUTER i.e. COM. Use of LEFT$ with FOR..NEXT CLS C$="NEPAL" FOR J=1 TO 5 L$= LEFT$(C$,J) PRINT L$; NEXT J END

276 GREEN Computer Book-8 Dry run helps you to understand how the program will be executed. J= 1 TO 5 L$=LEFT$(C$,J) Output (L$) NEXT J (J=J+1) 1 L$=LEFT$(“NEPAL”,1) N 1+1=2 2 L$=LEFT$(“NEPAL”,2) NE 2+1=3 3 L$=LEFT$(“NEPAL”,3) NEP 3+1=4 4 L$=LEFT$(“NEPAL”,4) NEPA 4+1=5 5 L$=LEFT$(“NEPAL”,5) NEPAL 5+1=6 FALSE 4. RIGHT$( ) This function returns specified number of characters from the right side of the supplied string. Syntax : RIGHT$(string, number) Example1 : RIGHT$("COMPUTER", 3) This returns three characters from the right of the string COMPUTER i.e. TER. Example2 : C$="COMPUTER" RIGHT$(C$,5) This will return five characters from the right of the string COMPUTER i.e. PUTER.ession Solved Example CLS C$="NEPAL" FOR J=1 TO LEN(C$) R$= RIGHT$(C$,J) PRINT R$ NEXT J END

GREEN Computer Book-8 277 Dry run helps you to understand how the program will be executed. J= 1 TO LEN(C$) R$=RIGHT$(C$,J) Output (L$) NEXT J (J=J+1) 1 R$=RIGHT$(“NEPAL”,1) L 1+1=2 2 R$=RIGHT$(“NEPAL”,2) AL 2+1=3 3 R$=RIGHT$(“NEPAL”,3) PAL 3+1=4 4 R$=RIGHT$(“NEPAL”,4) EPAL 4+1=5 5 R$=RIGHT$(“NEPAL”,5) NEPAL 5+1=6 5. MID$( ) This function returns specified number of characters from the specified position of a supplied string. Syntax : MID$(string, position, number) Example1 : MID$("COMPUTER", 4, 3) This will return three characters of the string COMPUTER starting from the fourth position of the string i.e. P. It will return PUT. Example2 : C$="COMPUTER" MID$(C$, 2, 4) This will return four characters of the string COMPUTER starting from the second position of the string i.e. O. It will return OMPU. Solved Example REM program to reverse a string C$="NEPAL" FOR J=5 TO 1 STEP -1 M$=MID$(C$,J,1) REV$=REV$+M$ NEXT J

278 GREEN Computer Book-8 PRINT "REVERSED STRING IS";REV$ END Dry run helps you to understand how the program will be executed. J= 5 TO 1 M$=MID$(C$,J,1) REV$=REV$+M$ Output (REV$) J=J-1 5 M$=MID$(“NEPAL”,5,1) “”+“L” 5-1=4 4 M$=MID$(“NEPAL”,4,1) “L”+ “A” 4-1=3 3 M$=MID$(“NEPAL”,3,1) “L”+“A”+“P” 3-1=2 2 M$=MID$(“NEPAL”,2,1) “L”+“A”+“P”+“E” 2-1=1 1 M$=MID$(“NEPAL”,1,1) “L” + “A” + “P” + “E” + “N” “LAPEN” 1-1=0 FALSE 6. LEN ( ) This function counts numbers of characters that are present in the supplied string. A space is counted as one character if there is space used in the string. It is a mathematical function. Syntax : LEN(string) Example1 : LEN("COMPUTER") This will count number of characters in the supplied string COMPUTER and returns 8 as there are eight characters in the string. Example2 : C$="QBASIC is a high level language" LEN(C$) This will count number of characters in the string including spaces. It will return 31. 7. SQR( ) This function returns square root of a supplied number. It is a mathematical function. Syntax : SQR(number) Example1 : SQR(25) This will return square root of 25 i.e. 5.

GREEN Computer Book-8 279 Example2 : N=100 SQR(N) This will return square root of 100 i.e. 10. Solved Example REM program to display the square root of a supplied number CLS INPUT "Enter a number"; N SQ=SQR(N) PRINT "Square root of "; N; " is ";SQ END 8. ASC( ) This function returns the ASCII value of a supplied character. ASCII stands for American Standard Codes for Information Interchange. There are 256 ASCII values ranging from 0 to 255 representing different characters, digits and symbols. Syntax : ASC(character) Example1 : ASC("A") This will return the ASCII value of the letter A. The letter A is represented by 65 in ASCII. So, it will return 65. Solved Example REM program to display A to Z CLS FOR J=64 TO 92 PRINT ASC(J), NEXT J END

280 GREEN Computer Book-8 POINTS TO REMEMBER 1. IF……….THEN……….ELSE is a conditional statement. 2. The combination of operators, variables and constants is known as an expression. 3. QBASIC Statement is the word used in QBASIC to perform specific task in a program. 4. CLS clears the screen each time you run the program. 5. REM statement is used throughout the program to explain what your code is trying to accomplish. 6. PRINT statement displays the value or values of variables on the screen. 7. Input allows user to enter value to variable during program execution. 8. Library Functions are the set of executable block of instructions capable of doing some specific tasks. 9. UCASE$ () function converts the supplied string to capital letters. 10. LCASE$() function converts the supplied string to small letters. 11. MID$() function returns specified number of characters from the specified position of a supplied string. 12. LEN() function counts numbers of characters that are present in the supplied string. Exercise 1. Write the syntax and purpose of the following statements and functions. a. INPUT b. PRINT c. IF…THEN….ELSE d. SELECT…..CASE e. LEN( ) f. MID$( ) g. LEFT$( ) h. RIGHT$( ) i. UCASE$( ) j. LCASE$( ) k. SQR( ) l. ASC( ) 2. Write a program for the following. a. To calculate area of a rectangle. [A=l x b] b. To calculate perimeter of a rectangle. [P=2( l + b )] c. To calculate area of a circle. [A=pr]

GREEN Computer Book-8 281 d. To calculate perimeter of a circle. [P=2pr] e. To calculate sum of two different numbers. f. To calculate product of two different numbers. g. To calculate difference of two different numbers. h. To input three different numbers and decide the smallest number amongst the three using IF…THEN statement. i. To input days of a week and decide “school day” or “holiday” using IF…THEN statement j. To decide whether an input number is divided by 5 and 3 or not? k. To input any number from 0 to 9 and check whether it is single digit number or not using SELECT CASE statement. l. To input name of the SAARC country and print name of their capital city using SELECT CASE statement. 3. WAP to perform the following using library function a. Write a program to return MAN from the word KATHMANDU. b. Write a program to return NEP from the word NEPAL. c. Write a program to return PAL from the word NEPAL. d. Write a program to return ASCII value of letter 'a'. e. Write programs to display following pattern: i. N NE NEP NEPA NEPAL ii. N E P A L NEPA NEP NE N f. Write a program to return RETUPMOC from the word COMPUTER.

282 GREEN Computer Book-8 22 Looping in Qbasic Looping is another name for iteration where a set of statements executes more than once. A loop is defined as a set of instructions that repeat a block of statements to the given number of times or till the given condition is satisfied or until a certain condition becomes true. Programming process jumps forwards and backwards in looping. A loop helps us to do more work with a lesser number of statements. There are three loop statements in QBASIC: 1. FOR ……….NEXT 2. WHILE ……………. WEND and 3. DO ………….. LOOP a. DO WHILE/ UNTIL……………..LOOP b. DO ……………LOOP WHILE/ UNTIL FOR ……….NEXT Statement Purpose: Repeats a block of statements for a specified number of times. Syntax: FOR counter = start TO End [STEP increment/ Decrement] [block of statement to be executed] NEXT counter Where, counter is a numeric variable used as the loop counter. Start and end are the initial and final values of the counter. Increment is the amount the counter is changed each time through the loop. More to know Use the CTRL+ pause break key to stop the infinite loop.

GREEN Computer Book-8 283 LAB Practice 1 CLS REM to print first 5 natural numbers. FOR CNT = 1 TO 5 PRINT CNT; NEXT CNT END LAB Practice 2 Write a program to print the sum of first 5 even numbers. CLS a=2 Sum=0 For i= 1 to 5 PRINT “Sum of the numbers:”; Sum Sum = Sum + a a=a+2 NEXT i END Dry Run a i Sum=Sum+a Sum(output) a=a+2 I=i+1 2 1 Sum=0+2 2 2+2=4 1+1=2 4 2 2+4 6 4+2=6 2+1=3 6 3 6+6 12 6+2=8 3+1=4 8 4 12+8 20 8+2=10 4+1=5 10 5 20+10 30 10+2=12 5+1=6 LAB Practice 3 REM to generate the following numbers 2,4,6,8,10,…50. CLS FOR I = 2 to 50 Step 2 PRINT I Dry Run CNT Output(CNT) CNT=CNT+1 1 1 1+1=2 2 2 2+1=3 3 3 3+1=4 4 4 4+1=5 5 5 5+1=6 False Note: If you don’t write step then qbasic suppose +1 itself

284 GREEN Computer Book-8 NEXT I END LAB Practice 4 REM generates the following numbers 5,10,15,…90 CLS FOR I = 5 to 90 Step 5 PRINT I NEXT I END WHILE …………WEND statement Purpose: Executes a series of statements as long as the specific condition is true. Syntax: WHILE condition Statement block WEND Flow chart of WHILE …..WEND statement Start Initial value of the counter Is the condition true? Yes No Stop Increase/Decrease the value of the counter Display output

GREEN Computer Book-8 285 Let us see an example to understand WHILE...WEND more clearly. LAB Practice 5 REM to print first 10 natural numbers. CLS I = 1 WHILE I<=10 PRINT I ; I = I + 1 WEND END LAB Practice 6 REM generates the following numbers 2,4,6,8,10….50 CLS I = 2 WHILE I < =50 PRINT I; I = I + 2 WEND END LAB Practice 7 REM to print numbers stated below 1,3,5,7,9,…99 CLS I = 1 WHILE I <=99 PRINT I; I = I + 2 Start I = 1 Is I < = 10 Yes No Stop I = I + 1 Print I

286 GREEN Computer Book-8 WEND END LAB Practice 8 REM to print numbers stated below1,4,9,…up to 10th term. CLS I=1 WHILE I < =10 PRINT I^2; I = I + 1 WEND END LAB Practice 9 REM to print numbers stated below10,9,8,7…up to 1. CLS I=10 WHILE I > = 1 PRINT I; I = I - 1 WEND END Exercise 1. Answer the following questions. a. What is looping? b. List out the types of loop statements in QBASIC. c. Write the purpose and syntax of FOR….NEXT statement. d. Write the purpose and syntax of WHILE…..WEND statement. e. What happens if you don’t write stem in FOR… NEXT statement?

GREEN Computer Book-8 287 2. Debug the following program: CLS CLS REM to print your name 5 times REM to print table of 9. INPUT “ Enter your name: $N P=9 FOR A= 1 TO 5 STEP -1 C=1 PRINT “My name is:”;$N WHILE C<=10 NEXT A T=P*C END PRINT T C=C-1 WEND END CLS REM to print length and entire character from third position of input string INPUT “Enter a string”; N$ L = LEN$(N$) ch= MID(N$, 3) PRINT L, ch END 3. Write a program for the following: a. To print multiplication table of 7.(eg. 7x1=7) [FOR..NEXT] b. To print your mother’s name 15 times. [WHILE…WEND] c. To print numbers from 15 to 1. [FOR..NEXT] d. To print sum of odd numbers between 2 and 20. [WHILE…WEND] e. To print the series 1, 8, 27…..up to 10th terms. f. To print the series 1,1,2,3,5,8……….up to 10th terms.

288 GREEN Computer Book-8 g. To print the following output: i. 5, 10, 15……up to 50 ii. 70, 65,60…..up to 10 iii. 5, 55, 555 up to 5th terms h. Write a program to print the following output of “NEPAL” i. N ii. N NE E NEP P NEPA A NEPAL L iii. LAPEN iv. NEPAL NEPA NEP NE N i. Write a program to print input string into reverse order.