Building Blocks 2 (1)

7/27/2019 Building Blocks 2 (1)

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For new comers,GWBASIC a good start-

easy to learn, portable executable programwith graphics capability, and is a freeware. BASIC-acronym for Beginners All-purpose

Symbolic Instruction Code designed as a language for beginners developed by John Kemeny and Kenneth Kurtz GWBASIC-version of BASIC produced by

Microsoft,Inc.

Other languages: FORTRAN - Formula Translation; for S and E. Gnu Fortran 77- freeware ; FORTRAN 90 is

most recent version.


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We will learn to write simpleprograms in GWBASIC

Gwbasic, Fortran and other higher level languagesdo essentially the same thing-they interpret theprogram or souce code we write into a languagethe machine can understand.

Gwbasic is a program by itself. It is an interpreter,that is, it translates our code line by line to thecomputer while our program is running.

Fortran and similar languages interpret or compilethe entire code into a machine language beforethe computer can run the program .


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GETTING STARTED

Beginning a session Gwbasic screen; KEY OFF, KEY ON

Coding or writing a new program (NEW) Saving a program (SAVE or F4 key) Loading or recalling a program (LOAD or F3

key) Running a program (RUN or F2 key) Ending your computer session (SYSTEM)


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Getting started- see how these

commands work. NEW SAVE filename

LOAD filename RUN filename SYSTEM

Note: close quotation optional. Extensionname if not present is understood to be .BAS.


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BUILDING BLOCKS OF AGWBASIC PROGRAM - 1

A Gwbasic program as shown in the examples is madeup of a structured collection of numbered LINESTATEMENTS, which are executed by the computer according to numerical sequence.

Structured means the line statements carry out specifictasks in accordance with some clear and logicalprocedure.

SYNTAXLine number statement [ : statement ] [ comment ]

Note:[ ] refer to optional elements in the line statement .


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BUILDING BLOCKS OF AGWBASIC PROGRAM - 2EXAMPLES OF LINE STATEMENTS

10 X = 5 : R = 8.03 : C=A*B C is the speed in cm/sec

300 Z = 2.98*(X+1.07)

500 PRINT X, Y, Z

600 GOTO 198

89 GOSUB 345

900 LPRINT A,B,C

40 IF X


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1. NUMERIC CONSTANTS - 1

TYPES OF NUMERIC CONSTANTS1. Integer - an ordinary integer, positive or negative.

Range -32768< x < 32768 .

Example 7, -23, 21346, +7892. Single precision - a number with six or fewer

significant digits that has a decimal point.

Range 10^(-38) < x < 10^(+38)(^ refers to exponentiation, meaning raised to)

Example 234.567, -9.8765, 6.023E+23


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1. NUMERIC CONSTANTS 23. Double precision a number with seven or more

significant digits and a decimal point. May have as

many as 17 significant digits.

Range As in single precision constants

Example 3.76324523, 0.9987698543574532,

1.6578438D-12


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1. NUMERIC CONSTANTS - 3TYPE DECLARATION TAGS

The type of a number can be indicated by a type

declaration tag:

TYPE TAG EXAMPLE

1. Integer % 3%, 564%

2. Single precision ! 1.34! , 43.7865!,

23.56E-83. Double precision # 3.4567#, 2.67D+21


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2. VARIABLES - 1

RULES FOR NAMING OF VARIABLES

1. Characters must be alphanumeric,i.e., usealphabetic (A-Z) and numeral (0 9) charactersonly.

2. First character must be a letter.3. Variable name may contain as many as 40

characters. No blank spaces in a name.

Note: Use variable names which reflect the data storedin the variable. Also, long variable names are notpractical or advisable to use in a program.


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2. VARIABLES - 2Variables in Gwbasic and other programming

languages are classified according to the data theystore. We have the following types in Gwbasic:

Variable type Type declaration tag Example

1. Integer % J%, KK%, ICT%2. Single ! X!, A7!, DIST!

3. Double # XJ23#, AREA#

4. String $ TITLE$, A5B$5. Note: String variables in Gwbasic are initialized to

the null character . The other variables areinitialized to 0.


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2. VARIABLES - 3

VARIABLE DECLARATION

1. Each variable must be assigned a type.

2. In general, however, it is not necessary to worryabout variable type declaration in a program.

Gwbasic adopts an implicit declaration of variables:variable names which end with the $ tag aredeclared string variables; variable names which donot end in any tag character are declared variable

names of type SINGLE.3. Explicit variable type declaration can be

accomplished using either the type declaration tags(%.!,#,$) or the DEFtype statements.


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2. VARIABLES - 4EXAMPLES EXPLICIT VARIABLE TYPE

DECLARATION

1. Using the tag characters A%, ITEM$, Y!, BBC#

2. Using the DEFtype statements put thesestatements at the beginning of the program.

DEFINT B-F, L-M, P This means that all variablenames which begin with the letters B to F, L to M,and P are to be treated as integer variables, that is,the values they store are integer constants.

DEFSNG, DEFDBL, DEFSTR statements for single,double, and string variables respectively follow thesame syntax.

Note: Tag characters override DEFtype statements.


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2. VARIABLES - 5SUBSCRIPTED VARIABLES

The purpose is to use the same variable name to refer toa collection of data or numbers.

Example: X(I), I = 1, 10

A(K , L ), K = 1,10 , L = 1, 25

Here , X is a one-dimensional array while A is a two-dimensional array. The dimensions or sizes of the arraysare communicated to the computer by using the DIMstatement:

10 DIM X(10), A(10,25)

Note:Put DIM statements at the beginning of theprogram.


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3. OPERATIONS - 11. 1. Hierarchy of operations: list is of descending

priority2. Operation Symbol Example

Exponentiation ^ 2^15, X^5,

5.12^(1/3)

Multiplication, division *, / X*Y, A/2.35

Integer division \ 3\2, 9\2

Remainder in integer MOD 8 MOD 3

division

Addition,subtraction +, - 6.7 +89.3 5.7


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3. OPERATIONS - 2

2. Arithmetic operations are carried out LEFT to RIGHT.

3. Use parentheses whenever their use will help clarifythe order of the operations that must be carried out.Inner parentheses are calculated first.

Examples3.6*89.2+6^3-8.7+2.3-1.9

((2.8-3.5*6)/3.9)-(2.7/3.8+43.3)

4. Algebraic expressions are constructed using thenumeric constants,variables and the arithmeticoperations discussed above. Built-in mathematicalfunctions in Gwbasic enlarge the kind of algebraic

expressions we can employ in a program.


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BUILT-IN FUNCTIONS - 1

FUNCTION SYNTAX1. Sine SIN(X) , X in radians

2. Cosine COS(X)

3. Tangent TAN(X)4. Arc tangent ATN(X)

5. Square root SQR(X) , X >= 0

6. Exponential EXP(X)7. Natural logarithm LOG(X) , X > 0


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BUILT-IN FUNCTIONS - 2FUNCTION SYNTAX

8. Absolute value ABS(X)

9. Greatest integer INT(X)

less than or equal

to X

10. Remove decimal FIX(X)

part of a number

11. Remove the number SGN(X)

but keep its sign


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BUILT-IN FUNCTIONS - 3

FUNCTION SYNTAX

12. Convert X to integer constant CINT(X)

13. Convert X to single precision CSNG(X)

constant

14. Convert X to double precision CDBL(X)

constant


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4. RULES

By this we mean the specific procedures that we mustuse in order to correctly translate our code into alanguage the computer can understand. We haveseen several of these rules.

Other rules relating to the various constructs of Gwbasic may be found in the appropriate sections of the manual you downloaded from the internet.


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5. STRUCTUREThe structure for the various commands will bediscussed when we get to them. However,the structureor layout of a Gwbasic program should look like the onebelow:

10 Program documentation

20 Main program

- dimension, type and user-defined function

statements

30 Subroutines

40 Data statements

50 End statement

INPUT/OUTPUT STATEMENTS 1


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INPUT/OUTPUT STATEMENTS - 1The purpose of these statements is to receive data for computer processing and to output the results generatedby the program.Input statements

1. INPUT - gets input data from keyboard.

100 INPUT X,Y, Z, AY$

20 INPUT IFLAG=; IFLAG

2. READ and DATA statements come together.

50 READ X, T, N$, H

100 DATA 10.3, 25.6, argon, 234.1


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INPUT/OUTPUT STATEMENTS - 2Output statements

1. PRINT - prints output to the screen.

100 PRINT A

50 PRINT TITLE$

350 PRINT TAB(5);X;TAB(15);Y

2. PRINT USING - for formatting output

120 PRINT USING ##.###;A

70 PRINT USING A= ##.### J=###;A,J

3. LPRINT - as above, but print is transferred to the

line printer for a hardcopy.

4. LPRINT USING - as in no. 3 above.


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CONTROL STATEMENTS - 1There are four control statements in Gwbasic: FOR-NEXT, GOTO, IF-THEN, and IF-THEN-ELSE.

1. FOR-NEXT - for repetitive calculations.

Syntax

line # FOR X = X1 TO X2 [STEP X3]

line # statement 1

line # statement n

line # NEXT X

Note: The default value of the increment X3 is 1 if the

optional bracketed expression is omitted.


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CONTROL STATEMENTS - 2Example : FOR-NEXT statement

120 FOR J = 1 TO 50

130 K = 3*J+1

140 PRINT J =;J;TAB(12);K =;K

150 NEXT J

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

20 SUM = 0. : KF%= 12 : KL% = 32 : KDEL% = 5

30 FOR K% = KF% TO KL% STEP KDEL%

40 SUM = SUM + 2.87*CSNG(K%)^3

50 NEXT K%


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CONTROL STATEMENTS - 3Example: nested FOR-NEXT statements

10 DIM A(50), B(50,20), C(50)

40 FOR N = 1 TO 30 STEP 3

50 X = A(N)^2 + 3.87

60 FOR L = 1 TO 10

70 B(N, L) = A(N)*C(L) *X + COS(X)/LOG(X-1.05)

80 NEXT L

90 NEXT N


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CONTROL STATEMENTS - 4

2. GOTO statement - for unconditional transfer of control Syntax

line # GOTO line #

Example120 GOTO 230

70 GOTO 10


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CONTROL STATEMENTS - 53. IF-THEN statement

Relational operators Symbol

Equal =

Less than

Less than or equal to =These operators are used in the argument of the IF

statement to determine the flow of control.


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CONTROL STATEMENTS - 6Compound relational operators: AND , OR

Simple relational expression - involves a singlerelational operator: A > 12, B8) AND (C8) OR (C


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Building Blocks 2 (1)

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