NOS : Certificate in Computer Applications
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In the previous lesson, we studied about the constants, the variables and the arithmetic operation used in the BASIC language. We also saw how these constants, variables and the arithmetic operations may be combined to form expressions and statements. Now we shall learn how the complete program in BASIC language can be written using the basic principles we have learnt so far.

For a computer program to be executed using a computer, we should give some values to the computer. Once the computer, completes the required computation work, we should ask the computer to produce the results in a proper format that can be understood by the common man. The INPUT/OUTPUT statements of the BASIC language achieve these two important functions. Besides these we shall also discuss the use of repetitive and branching statements used in BASIC language.

At the end of this lesson, you should be able to:

• understand clearly the use of INPUT/OUTPUT statements such as LET, READ-DATA, INPUT, PRINT, PRINT USING etc.
• learn the use of LOOPING and CONTROL statements.
• develop BASIC programs using the various basic commands offered by the language

It should be always kept in mind that computer cannot do anything by itself. It will act according to the instructions supplied to it by the user. To achieve the required output in the desired format, a user has to provide correct data and a series of processing instructions in proper order. In this section, we will discuss various input/output statements provided in BASIC language.

As stated earlier, one of the basic features of a programming language is the input/output facility offered by it. BASIC offers three such kinds of input statements. They are LET, INPUT and READ-DATA. These statements are basically used to assign values to various variables.

Syntax:

Line number LET (variable name)=(Constants or Variables or expression)

Example of LET statement

10 LET X =5.32 ---> This is numeric constant

20 LET A = 6+9/3.2--> This is an arithmetic expression

30 LET Y = X+A --> This is also an arithmetic expression

40 LET I = F ²-->numeric constant

50 LET I =I+Y -->I and Y are variable names

60 LET A$ = "NEW DELHI"--> String variable

70 LET F$ = "99983" -->String variable

80 LET A = B--> numeric variable

These are all valid LET statements. The value of the variable on the left hand side of the equal to sign is assigned the value given in the right hand side of the equal to sign

15 LET A =10

25 LET B =5

35 LET A = A+B

The example shows A is the variable name, which is, assigned the value 10 and B is the variable name assigned the value 5. In the memory the line number 15 gives an instruction by which A will be the address or name of a cell/location where the value 10 will be stored. Similarly B will be name or address of a cell/location where 5 will be stored. Line number 35 instructs that the values in the address A and B be added and the resulting value be kept at the cell/location whose address is A.

Note here that after execution of line 15 it has been shown "Not known" in location B, because in this program we have not given any value to the variable name B on line number 15. It's value is given in the next line number 25. Since variable A has been already given the value 10 that continue to stay in A until we assign a different value to A which replaces the earlier value. So in the next line number 35, A+B the values of A and B given before are added and put in the location A Now the latest value of A is 15 and that of B will remain as 5. Let us suppose that line 35 has been replaced as

35 LET C = A + B

Here computer will add the values of A and B, i.e. 15 and put it in a third location C.

Line number INPUT Variable,List...

12 INPUT A,B,X

16 INPUT A$,F$,N$

20 INPUT Y1,F$,C2,NB

Whenever computer reads a line with the keyword INPUT it displays a sign? on the VDU and waits for the data. We have to give the values of the variable at this prompt through the keyboard.

The LET and INPUT statement have certain limitations. By a LET statement we can assign one value for each variable and if we have to get 10 values for 10 variables we have to use 10 statements with LET. Also if a value is assigned through a LET statement its value can be changed only by replacing that assignment statement by another assignment statement. In case of an input statement, the data is provided at the prompt at execution time. If there is a large amount of data to be processed, it is inconvenient to key in the entire data during the execution of the program. In such cases READ statements are found useful. READ statement will always have a DATA statement along with it.

Line number READ Variable, List....

Line number DATA Constant, List....

Example of a READ....DATA Statement

1 REM PROGRAM EXPLAINING READ....DATA STATEMENT

5 READ X2,Y,Z1,K

9 READ A,B3, C4, L

22 DATA 8,9,13,15,16,51,30,92

30 END

When the machine encounters the line number 5 with the READ statement followed by the variables X2,Y,Z1,K it will collect from the DATA statements the values for these variables in the same order. A one-to-one correspondence exists in READ-DATA statement, i.e. X2=8, Y=9, Z1=13, K=15.

In the next READ statement in line number 9 we have four more variables A,B3,C4,L.

These values will follow in the same order and one-to-one correspondence after the earlier READ variables values, i.e., after 8,9,13,15, i.e., A=16, B3=51, C4=30, L=92.

Since all the values in the DATA here are exhausted, another i.e. third, READ statement cannot be used until another DATA statement is included or more DATA is included in the above DATA list in line number 22. A DATA statement can be anywhere in the program but must be before the END statement. It is a normal practice to keep all DATA statements together at the end of the program before END statement, so that in case you want to alter any data at the end it will be easy.

The BASIC organises the contents of all the DATA statements into a data block. When the READ statement are executed a pointer moves along with data block starting from the first element:

1 READ X1, Y1, Z1

7 READ N, M, L, K

12 READ A

19 READ X,Y

24 DATA 122

26 DATA-35,49, -101

28 DATA -691,81

30 DATA 8,10.-5,5

40    END

DATA BLOCK

Value	Pointer	Variable
122		X1
-35		Y1
49		Z1
-101		N
-691		M
81		L
8		K
10		A
-5		X

Now look at the following some examples where all the programs do exactly the same work.

(a)

10 DATA "RAMA","DELHI",100,200,300

20 READ A$,B$,A, B, C

30    - - - - -

40 - - - - -

       - - - - - - - - - - - - - -

80 END

(b)

10 READ A$,B$

20 READ A,B,C

30 - - - - - -

40 - - - - - -

60 DATA "RAMA","DELHI"

70 DATA 100,200,300

100 END

(c)

10 DATA "RAMA","DELHI"

20 DATA 100

30 DATA 200

40 DATA 300

50 READ A$,B$

60 READ A,B,C

- - - - - - - - - - - - -

100 END

(d)

10 READ A$

20 READ B$,A,B,C

30 DATA "RAMA"

40 DATA "DELHI"

50 DATA 100,200,300

- - - - - - - - - - - - -

100 END

In all these cases A$ is assigned the value RAMA and B$ the value DELHI.All the numeric variables A,B,C are assigned the values 100,200,300 respectively.

So we note that for READ....DATA statement we should follow the following

• There could be any number of READ and DATA statements.
• As many variables are read by READ statement, at least the same number of values should be there in the DATA statement. It may be more. If the number of values in DATA is less, then there will be an error message OUT OF DATA given by the computer.
• The type of variables (i.e., numeric, string) in the READ statements containing many variables.
• Although normally we keep all the DATA statements at the end of the program just before END statement, DATA statement can occur anywhere in the program but before END statement.

The RESTORE statement beings the pointer to the first value of the DATA statement regardless of the current position of the pointer.

Line number RESTORE

For example,

10 RESTORE

The RESTORE statements may be used anywhere in the program, of course, before the END statement.

The following example will clearly illustrates the use of RESTORE statement

10 READ X,Y

20 DATA 10,12,-7,,3.2, "PANKAJ"

30 RESTORE

40 READ A,B,C,D,N$

50 END

When the statement number 10 is executed, the variables X and Y are assigned the values of 10 and 12, the position of the pointer at this stage is shown below:

10 12 -7 3.2 "PANKAJ"

­ (Pointer)

(Position of pointer before execution of RESTORE statement)

When the statement 30 RESTORE is executed, the pointer is brought back to the first data value of data statement as shown below:

10 12 -7 3.2 "PANKAJ"

                    ( Pointer)

Now, the execution of the statement number 40 against the value to A,B,C,D and N$ will be as shown below:

A 10

B 12

C -7

D 3.2

PANKAJ

The RESTORE statement can be used in the following forms also:

Statement number RESTORE *

and

Statement number RESTORE $

If the key word RESTORE is followed by asterisk (*), then only numeric pointer is reset as shown in the previous example. However, if the key word RESTORE is followed by a dollar sign ($), then only string pointer is reset to the first string data. The simultaneous use of both asterisk (*) and dollar sign ($) is not allowed.

For example, if a BASIC program contains the following statements,

10 READ A,B,N$,M$

20 - - - - - - -

30 - - - - - - -

40 RESTORE *

50 READ P,Q,A$,B$

60 - - - - - - -

70 - - - - - - -

80 DATA 5,8,"DINESH",UPMA",10,12,"RAJESH","SANJU"

90 END

When the statement 10 is executed, A,B are assigned values 5 and 8 whereas the variables N$ and M$ are assigned the values DINESH and UPMA respectively. The execution of statement 40, restores the numeric pointer to the first numeric value in the DATA statement i.e. to the value 5. The execution of the statement 50, assigns the value 5,8, RAJESH and SANJU respectively to the variable P,Q,A$ and B$. The values DINESH and UPMA are being ignored. Similarly, the execution of RESTORE$ can also shown by taking similar example.

Consider another example

10 READ A,B,N$,M$

20 RESTORE $

30 READ P,Q,A$,B$

40 DATA 5,8, "DINESH", "UPMA", 10,12,"RAJESH",SANJU"

50 END

Here the statement RESTORE$ is used. The values assigned to the variable A,B,N$ and M$ are same as in the previous example. However, when statement 20 is executed, the string pointer is reset to the first string data namely DINESH. The execution of the statement 30 would assign the values 10 and 12 to the variables P and Q and then the pointer moves back-ward to assign the values DINESH and UPMA to the variables A$ and B$

The PRINT statement of BASIC provides limited methods of controlling the alignment and spacing of printout in terminals. The general from of the PRINT statement is

Line number PRINT (Variable) separator (variable) separator or item......

The separation may be comma (,) or semicolon (;)

Program

10 LET S =1175.50

20 PRINT "TOTAL SALARY =";S; " RUPEES"

30 END

The output of the program 1 will be as

Using semicolon in a print statement, the items are close to each other, and as a result more items can be printed in one line,

100 PRINT "NUM","TEMP","SIZE", REMARK"

110 PRINT 65,-15.56,36,34

These two lines will be printed as follows

1 17 33 49 65 85

The number of columns in each zone may be checked from the literature of manual for the given computer.

The PRINT USING statement is included in most versions of microcomputer BASIC. It allows printed output to be formatted, giving the appearance of each data item. This PRINT USING statement can specify both string and numeric data.

There are several different ways to format. The most commonly used are given below:

100 PRINT USING "##. ##"; A,B,C,

Line number PRINT USING Format String Numeric Variables

The format string "##. ##", which a numeric field containing a decimal point with not more than two digits on each side.

What will be the output of the following program?

10 LET A =17.32

20 LET B = -5.38

30 LET C =40

40 PRINT USING "##. ##",A,B,C,

50 END

17.32 -5.38 40.00

If string values are used instead of numeric values, the format string for PRINT USING will be as follows:

100 PRINT USING "!!!!!!" ; N$

If N$ ="UNITED"

Then the above PRINT USING statement will give output as:

UNITED

Observe, there are six alphabets and we have used six exclamation sign (!). Each exclamation sign (!) is used to represent each character of a string.

Note: Some computers use # for presenting a character.

If N$ = "FROG" then

(a) 100 PRINT USING "!!!!";N$ gives output as bbFROG

(b) 100 PRINT USING ">!!!!!!";N$ gives output as

(> character is used for the right justification of a string.)

Since "!!!!!!" has six character representations and FROG has only four characters,">" sign gives characters b b in the left side as the PRINT USING with > gives right justified. Space characters (b b ) are used to fill left space.

With the same explanation

100 PRINT USING "<!!!!!!"; N$ gives output FROG b b

(< is for left justified), Left justified space filled to right.

Note: b is used as space character.

26.4.4 TAB FUNCTION

The TAB (abbreviation of TABULATION) function is a very important function because it enables the user to exercise exact control over the print positions. The use of a COMMA and a SEMICOLON to space out the output is not so flexible as the TAB function.

TAB (n) moves the printer head to the n^th column and printout of any data starts from that column.

Syntax:

Line number PRINT TAB (N); X

Where N is a positive number, a variable or an expression having positive value and X shows output data

The execution of TAB function is explained below:-

( i ) If N is an integer, the printer head moves to the Nth column and printing of the value of X starts from that column

( ii ) In case N is a variable, not having the internal value, it is rounded and the printer head moves according to this value.

For example, 5 X = 12

1. K = 5.3

20 PRINT TAB(k) ; X

( iii ) On the other hand, if N is an expression then first of all, the expression is evaluated and rounded, if necessary. The printer head move based on the value of this expression.

The backward movement of the printer head is not allowed.

For example, consider the statement

10 PRINT TAB (25); "DINESH"; TAB(20); "RAJESH"

Here TAB (25) instructs the computer to start printing DINESH from column number 25 onwards. Then TAB (20) instructs the computer to write RAJESH from column 20. Since the printer head is already beyond the column 20 and backward movement is not allowed, so TAB (20) is ignored and the output is same as if TAB (20) was not present. The above statement is equivalent to

10 PRINT TAB (25); "DINESH"; "RAJESH"

Consider another example, where TAB function is ignored

20 PRINT "10.3", TAB (10); "15.6"

The comma preceding the function TAB (10) Positions the printer head to the column 16 so that the function TAB (10) becomes redundant as printer head cannot move backward and hence it is ignored. The value 15.6 will be printer from column 16 onwards.

The use of TAB function is an elegant method to prepare patterns, producing tables and to plot graphs etc.

We have already seen a few BASIC statement like REM, (in Lesson 1),and LET,INPUT,READ,DATA etc in this Lesson itself. The other few BASIC statements and their explanations are given in this section. We will discuss them in details using different program.

GOTO statement is used to transfer control from a statement, say S1 to another statement, say S2, generally, S2 does not follow S1 immediately in sequence.

Syntax: Line number GO TO n

n is the line number of the statement where control will be transferred.

Program 1

10    READ A,B,X,Y

20 GO TO 60

30 LET X = X*X+A

40 LET =Y*Y +B

50 PRINT X, Y

60 LET X =A*X

70 LET Y =B*Y

80 PRINT X,Y

90 DATA 6,3,4,5

100 END

This shows after reading the values of A,B,X,Y, in line number 10, the control jumps to line number 60 and calculate X =A*X, Y =B*Y then prints X,Y in line number 80 and ends the program. Line number 30,40,50 are never executed. If we want to execute 30,40,50 then our program will add few more jump statements, i.e. few more GO TO statements.

Consider the following program 2.

10 READ A,B,X,Y

20 GO TO 60

30 LET X =X*X+A

40 LET Y =Y*Y+B

50 PRINT X,Y

55 GO TO 100

60 LET X =A*X

70 LET Y =B*Y

80 PRINT X,Y

85 GO TO 30

90 DATA 6,3,4,5

100 END

Thus by introducing line number 55 and 85 all the statements are executed. So line number 30 and 40 prints X =X*X +A (value), Y =Y*Y+B (value) and line number 80 prints X = A*X and Y =B*Y

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IN-TEXT QUESTION1

1. Fill in the blanks

1. In the LET statement, the value of a variable on the ......... hand side of the equal to sign is assigned to the variable given in the .......... hand side of the equal to sign.
2. READ statement cannot be used without a ........... statement.
3. DATA statement can occur anywhere in the program, but must be before the ........... statement.

2. State the difference between READ and INPUT statement?
3. What is the use of PRINT USING statement?
4. What is the use of RESTORE statement?
5. Define briefly the use of TAB function.

The IF...THEN is a decision making statement, depending upon the decision, it can change the order of execution.

It helps the computer to check whether a relation is TRUE or FALSE.

Syntax: Line number IF (relational expression) THEN n where n is a line number or an instruction itself.

If the relation expression is true then n will be executed otherwise the statement following this IF...THEN statement will be executed.

Evaluate the expression Y =X² for X =1,2,3...

10 LET X = 1

20 LET Y = X*X

30 PRINT Y

40 LET X = X+1

50 GO TO 20

60 END

In this process we see each time the line number 50 is executed the control is transferred to line number 20 unconditionally. Thus we have an infinite loop which is never ending.

Computer goes round and round and never reaches END

To stop the infinite loop we can add a condition, i.e. say if X is greater than or equal to 31 (X >=31) then the program ends otherwise it keeps on printing the value of expression Y = X² for X =1,2,3....30.

10 LET X = 1

20 LET Y = X*X

30 PRINT Y

40 LET X = X+1

50 IF X> = 31 THEN 70

60 GO TO 20

70 END

Thus we see that IF-THEN is one of the powerful statements which can stop or get the computer out of an infinite loop.

Write a program to find out the auto fare depending on the Kilometers traveled. The minimum fare charged is Rs. 3.00. This minimum fare remains for 2 kms or less of travel. After 2 kms, the charges are 75 rp per kilometer.

10 INPUT "KILOMETER", K

20 IF K < = 2 THEN PRINT "RS.3" : END

30 LET CHARGE =3+ (K-2) *.75

40 PRINT CHARGE

50 END

Here in line number 20, if K is less than or equal to 2 (i.e., K<=2) then it will print Rs. 3 and (: END) means END, in continuation to the line number 20 next statement is END.

Otherwise if K is not less than or equal to 2 then line number 30,40 then 50 will be executed.

Another important statement is IF ...THEN...ELSE.

Syntax:

Line number IF (condition or relational expression)

THEN (line number or Instruction)

ELSE (line number or Instruction)

The IF...THEN...ELSE statement is a decision making statement as it decides the path of the program. It helps in making comparisons and testing whether a condition is true or not.

IF is always followed by a valid BASIC condition or expression. If the condition is found true then the line number or Instruction after THEN is performed otherwise line number or instruction after ELSE is performed.

EXAMPLE 4

Ages of different students appearing in the Board examination are taken. If the age is below 17 the student is not eligible, otherwise he can appear in the Board examination. We are asked to write a program for this problem.

10 INPUT "AGE"; A

20 IF A>= 17 THEN 30 ELSE 50

30 PRINT "WELCOME FOR BOARD EXAMINATION"

40 GO TO 60

50 PRINT "YOU ARE NOT ELIGIBLE FOR BOARD EXAM."

60 INPUT "WANT TO INPUT AGAIN (Y/N)"; Y$

70 IF Y$ = "Y" THEN 10

80 END

The line number 10 will cause the message in screen AGE? We input the age through the keyboard, say 18. Line number 20 tests whether A>17 or not. Since A=18>17 line number 30 is executed.

Line number 30 prints WELCOME FOR BOARD

Line number 40 causes the control to pass to line number 60.

Line number 60 causes the message WANT TO INPUT AGAIN (Y/N)? We input either Y or N.

In line number 70 if input is Y then control goes to line number 10. Otherwise if input is N then control goes to the line number 80 i.e. END.

Now if in line number 70 we input Y then control will pass again line number 10, we give another age, say 13

In line number 20 value of A (i.e. 13) is not greater than 17, therefore ELSE part will be executed and control will go to line number 50. Line number 50 will print YOU ARE NOT ELIGIBLE FOR BOARD EXAM. Then line number 60 as before will be executed. In this way a large number of students age can be tested. When we want to stop we should input N in line 60 for Y$.

10 INPUT A,B,C

20 IF A>B AND A>C THEN 50 ELSE 30

30 IF B>A AND B>C THEN 60 ELSE 40

40 IF C>A AND C>B THEN 70

50 PRINT "A IS THE LARGEST NUMBER": GO TO 80

60 PRINT "B IS THE LARGEST NUMBER": GO TO 80

70 PRINT "C IS THE LARGEST NUMBER"

80 INPUT "WANT TO INPUT AGAIN (Y/N)" ; Y$

90 IF Y$ = "Y" THEN 10

100 END

In line number 20,30,40 comparisons are made among the values of A,B, and C.

AND is a logical operator which combines A>B and A>C. If both the relational expression preceding and following AND are true then the line number following THEN will be executed otherwise if one of the relational expression, A>B or A>C is true then the line number following ELSE will be executed. Same procedure follows for the next two IF statements also.

If expression at 20 is found true, the line number 50 will print A is THE LARGEST VALUE and then GO TO 80 will be executed as the next statement to line number 50. If it is found false the control passes to statement 30 and the expression at that statement is checked. This part of the program can also be written as follows:

50 PRINT "A IS THE LARGEST NUMBER"

55 GO TO 80

60 PRINT "B IS THE LARGEST NUMBER"

65 GO TO 80

Thus line number 50 and 60 in earlier program of problem 2 is equivalent to line numbers 50,55,60,65 in the above program statement.

Syntax: For IF...THEN...ELSE with AND is given as;

IF (Condition 1 or Relational expression) AND (Condition 2 or Relational expression) THEN (Instruction 1) ELSE (Instruction 2)

Like AND another logical operator is OR.

Syntax: for IF…. THEN...ELSE with OR is:

IF (Condition 1 or Relational expression) OR (condition 2 or Relational expression)

THEN (Instruction 1) ELSE (Instruction 2)

This means if either of the conditions (or relational expression) followed or preceded by OR is true then the instruction 1 is executed. If neither of them is true then instruction 2 is executed.

We have already seen that a loop can be built in BASIC by using the IF-THEN and GOTO statements.

When it is known in advance how many times the loop must be repeated the statement FOR-TO...NEXT is the most effective statement.

A loop is built up by FOR-TO and ended by NEXT.

Syntax:

           Line number FOR I = M TO N STEP J

Loop ----------------------------------------------

Line number NEXT I

The numeric variable name following FOR is called the control variable or loop variable.

M and N are numeric constants where M gives the initial or starting value of the loop and N gives the final value, J followed by keyboard STEP gives the increment in M till N is reached. The increment can be negative also.

M,N,J can be numeric variable names. In such cases their numeric values should be assigned before the starting of the loop, i.e. before coming to FOR-TO statement.

They key word NEXT should have the same control variable I followed by it. Thus one loop can be started with FOR-TO and ended with NEXT.

Inside one FOR-TO ...NEXT loop there can be more FOR-TO...NEXT loop. But once a FOR-TO...NEXT is inside another FOR-TO...NEXT, it should remain completely inside the former loop. Such FOR-TO...NEXT loops are called Nested loops. In the absence of the STEP clause, the increment is assumed to be 1.

Suppose we want to print the output in the following format:

* * * * *
* * * *
* * *
* *
*

10 FOR S=5 TO 1 STEP-1

20    FOR X=1 TO S

30 PRINT "*" ;

40 NEXT X

50 PRINT

60 NEXT S

70 END

This program contains two loops: the outer loop is from the line number 10 to 60 and inner loop from line numbers 20 to 40. In line number 10, initially S is assigned a value 5. Since the value of S is greater than 1, control is transferred to line number 20, which causes the inner loop to execute 5 times resulting into printing of 5 stars (*) in one row. The statement at line number 50 will transfer the printer control to the beginning of the next line. When line 60 is encountered, the control goes back to line number 10. Now the value of S becomes 4 and once again the inner loop is executed 4 times resulting in printing of 4 (*) stars in second row. This process will continue till the value of S becomes 1. After that it will come to end.

Suppose we want to sum to following series:

1,2,3,4_ _ _ _ 100.

10 LET S=0

20 FOR I=1 TO 100

30 LET S=S+I

40 NEXT I

50    PRINT " SUM OF SERIES =" ; S

60    END

The GOTO statement allows only one transfer point, IF...THEN allows two transfer points, the ON...GOTO can have more than two transfer points, thus providing multiple branching facility.

Syntax: line number ON (Numeric variable or expression) GOTO n1,.n2,n3,..

The expression is a valid BASIC expression and n1,n2,n3,.... are the statement numbers or line number where the control will be transferred.

If ON is followed by numeric variable name and if the value of numeric variable is 1 control is transferred to n1, if 2 then n2, if 3 then n3 and so on.

If ON is followed by an expression by an expression then it is evaluated and truncated to an integer value. Control is transferred in the same manner as discussed above.

If the integer value is less than or more than number of line numbers present in the list then an "OUT OF RANGE" error message will be given by the computer.

Write a program to add, subtract, divide and multiply two numbers A and B.

5 INPUT A,B

10 INPUT " 1-ADD, 2-SUB, 3-MUL, 4-DIV"; N

20 ON N GOTO 30,40,50,60

30 PRINT A+B : END

40 PRINT A-B : END

50 PRINT A*B : END

60 PRINT A/B : END

When line 5 is executed, there will be question mark (?) then you have to input the values of A and B through keyboard. Line number 10 will cause a message on the screen 1-ADD, 2-SUB, 3-MUL, 4-DIV and then display of question mark (?) for N.

If we input through keyboard 1 then N takes the value 1.If we enter 2 or 3 or 4,N will take 2 or 3 or 4 accordingly. If the value of N is

1 control is transferred to 30,

2 control is transferred to 40,

3 control is transferred to 50,

4 control is transferred to 60

On execution of line number 30 addition of A and B will be displayed on the screen and program will come to an end. Similarly, in line number 40,50,60 printing of the result of subtraction, multiplication and division will be displayed respectively.

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1. Write a LET statement for each of the following:

(a) To assign the value 5.2 to the variable A

(b) To assign the string PENTIUM-SYSTEM TO the variable B$

(c) To assign the value of the variable C to the variable D

(d) To increase the value of the variable E by 1

(e) To assign the value equal to three times the value of the variable P to the variable Q

2. In the following FOR statements, write the values taken by the control variable

(a) 10 FOR L = 3 TO 12 STEP 2

(b) 20 FOR M = 1 TO 50 STEP 10

(c) 30 FOR N = 100 TO 0 STEP -20

(d) 40 FOR K = 5 TO 5

(e) 50 FOR I = 10 TO 6 STEP -1

3. Give the output of the following short program

10 PRINT "PANKAJ" , "GOEL"

20 PRINT "PANKAJ" ; "GOEL"

30 PRINT "PANKAJ",, "GOEL"

4. Give the output of the following short program

10 LET A = 40

20 LET B = 50

30 LET C = 60

40 LET D = A+B+C

50 PRINT "A= A"; A "B = B"; B "C="; C, "D="; D

60 END

This lesson gives us the introductory features of BASIC language, which are very essential for writing small programs in BASIC. Some additional statements and functions of BASIC will be discussed in Lesson 4. The example programs given in this lesson should be run on a computer so that the concept is clear before going to the next lesson.

1. What does an unconditional GOTO statement do?
2. What is the difference between an IF... THEN statement and an IF... THEN... ELSE statement?
3. How is the multiple branching facility provided in BASIC?
4. Write a program in BASIC using For-Next loop to get the following output:

1 * * * *

2 * * * * * * * * * *

3 * * * * *

4 * *

5 * * * * * * *

5. Write a program in BASIC to print out the largest number out of 10 given numbers.

IN-TEXT QUESTIONS 1

1.

(a) Right, Left

(b) DATA

(c) END

2. In case of an INPUT statement, data is read from the keyboard at the time of execution of the program. In READ statement, data is provided in the program itself through a DATA statement.
3. Print using statement allows printed output to be formatted corresponding to the given specification.
4. The restore statement brings the pointer to the first value of the DATA statement, regardless of the current position of the pointer.
5. TAB function enables the user to exercise exact control over the print positions.

IN-TEXT QUESTIONS 26.2

1.

(a) 10 LET A = 5.2

(b) 20 LET B$="PENTIUM-SYSTEM"

(c) 30 LET D = C

(d) 40 LET E = E+1

(f) 50 LET Q =3*P

2

(a) Values taken by L are : 3,5,7,9,11

(b) Values taken by M are : 1,11,21,31,41,

(c) Values taken by N are : 100,80, 60,40,20,0

(d) Value taken by K is : 5

(e) Values taken by I are : 10,9,8,7,6,

3.

PANKAJ GOEL

PANKAJ GOEL

PANKAJ GOEL

4.

A= 40 B= 50 C= 60 D =150

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