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Building blocks No. 2and GWBASIC PROGRAMMING

- For new comers,GWBASIC a good start-easy to

learn, portable executable program with 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.

We will learn to write simple programs in GWBASIC

- Gwbasic, Fortran and other higher level languages

do essentially the same thing-they interpret the

program or souce code we write into a language

the machine can understand. - Gwbasic is a program by itself. It is an

interpreter, that is, it translates our code line

by line to the computer while our program is

running. - Fortran and similar languages interpret or

compile the entire code into a machine language

before the computer can run the program.

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)

Getting started- see how these commands work.

- NEW
- SAVE filename
- LOAD filename
- RUN filename
- SYSTEM
- Note close quotation optional. Extension name if

not present is understood to be .BAS.

GWBASIC EDITOR

- A Gwbasic pgm consists of numbered program lines

all lines are executable except REM (or ) lines.

The lines are executed according to numerical

sequence. - Correcting errors-key operations
- Inserting lines
- Some commands for editing
- CLS, FILES, LIST
- RENUM, DELETE

BUILDING BLOCKS OF A GWBASIC PROGRAM - 1

A Gwbasic program as shown in the examples is

made up of a structured collection of numbered

LINE STATEMENTS, which are executed by the

computer according to numerical

sequence. Structured means the line statements

carry out specific tasks in accordance with some

clear and logical procedure. SYNTAX Line number

statement statement comment Note

refer to optional elements in the line

statement.

BUILDING BLOCKS OF A GWBASIC PROGRAM - 2

EXAMPLES OF LINE STATEMENTS 10 X 5 R 8.03

CAB C is the speed in cm/sec 300 Z

2.98(X1.07) 500 PRINT X, Y, Z 600 GOTO 198 89

GOSUB 345 900 LPRINT A,B,C 40 IF Xlt2 THEN GOTO

30 ELSE GOTO 90 10 REM Program does linear

regression analysis.

BUILDING BLOCKS OF A GWBASIC PROGRAM - 3

QUESTION What makes up a line statement? How do

we construct them? 1. NUMERIC CONSTANTS - 2, 1/4,

-56.083, 0.000367, -3.45E12, 12.9213,

6.213453678921234 2. VARIABLES - X , Y, DIST ,

A(2), B(3,4), NAME 3. OPERATIONS -

arithmetic/algebraic operations , -, ,

/ ,\ , MOD 4. RULES - naming of variables,

hierarchy of operations, use of parentheses,

... 5. STRUCTURE - flow of control, program

layout, ...

1. NUMERIC CONSTANTS - 1

TYPES OF NUMERIC CONSTANTS 1. Integer - an

ordinary integer, positive or negative.

Range -32768lt x lt 32768 . Example 7, -23,

21346, 789 2. Single precision - a number with

six or fewer significant digits that has a

decimal point. Range 10(-38) lt x lt

10(38) ( refers to exponentiation,

meaning raised to) Example 234.567,

-9.8765, 6.023E23

1. NUMERIC CONSTANTS 2

3. 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

1. NUMERIC CONSTANTS - 3

- TYPE 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-8
- 3. Double precision 3.4567,

2.67D21

2. VARIABLES - 1

- RULES FOR NAMING OF VARIABLES
- 1. Characters must be alphanumeric,i.e., use

alphabetic (A-Z) and numeral (0 9) characters

only. - 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

stored in the variable. Also, long variable names

are not practical or advisable to use in a

program.

2. VARIABLES - 2

- Variables in Gwbasic and other programming

languages are classified according to the data

they store. We have the following types in

Gwbasic - Variable type Type declaration tag

Example - Integer J, KK, ICT
- Single ! X!, A7!, DIST!
- Double XJ23,

AREA - String TITLE, A5B
- Note String variables in Gwbasic are initialized

to the null character . The other variables

are initialized to 0.

2. VARIABLES - 3

- VARIABLE DECLARATION
- Each variable must be assigned a type.
- In general, however, it is not necessary to worry

about variable type declaration in a program.

Gwbasic adopts an implicit declaration of

variables variable names which end with the

tag are declared string variables variable names

which do not end in any tag character are

declared variable names of type SINGLE. - Explicit variable type declaration can be

accomplished using either the type declaration

tags (.!,,) or the DEFtype statements.

2. VARIABLES - 4

- EXAMPLES EXPLICIT VARIABLE TYPE DECLARATION
- Using the tag characters A, ITEM, Y!, BBC
- Using the DEFtype statements put these

statements at the beginning of the program.

- DEFINT B-F, L-M, P This means that all

variable names 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 the same syntax. - Note Tag characters override DEFtype statements.

2. VARIABLES - 5

SUBSCRIPTED VARIABLES The purpose is to use the

same variable name to refer to a 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

arrays are communicated to the computer by using

the DIM statement 10 DIM X(10),

A(10,25) NotePut DIM statements at the beginning

of the program.

3. OPERATIONS - 1

- 1. Hierarchy of operations list is of descending

priority - Operation Symbol Example
- Exponentiation

215, X5, -

5.12(1/3) - Multiplication, division , /

XY, 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

3. OPERATIONS - 2

2. Arithmetic operations are carried out LEFT to

RIGHT. 3. Use parentheses whenever their use will

help clarify the order of the operations that

must be carried out. Inner parentheses are

calculated first. Examples 3.689.263-8.72.3-1

.9 ((2.8-3.56)/3.9)-(2.7/3.843.3) 4. Algebraic

expressions are constructed using the numeric

constants,variables and the arithmetic operations

discussed above. Built-in mathematical functions

in Gwbasic enlarge the kind of algebraic

expressions we can employ in a program.

BUILT-IN FUNCTIONS - 1

FUNCTION SYNTAX 1. 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 gt 0 6. Exponential

EXP(X) 7. Natural logarithm LOG(X) , X

gt 0

BUILT-IN FUNCTIONS - 2

FUNCTION 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

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

4. RULES

By this we mean the specific procedures that we

must use in order to correctly translate our code

into a language the computer can understand. We

have seen 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.

5. STRUCTURE

The structure for the various commands will be

discussed when we get to them. However,the

structure or layout of a Gwbasic program should

look like the one below 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

The purpose of these statements is to receive

data for computer processing and to output the

results generated by 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

INPUT/OUTPUT STATEMENTS - 2

Output statements 1. PRINT - prints output to

the screen. 100 PRINT A 50

PRINT TITLE 350 PRINT

TAB(5)XTAB(15)Y 2. PRINT USING - for

formatting output 120 PRINT USING

.A 70 PRINT USING A .

JA,J 3. LPRINT - as above, but

print is transferred to the line

printer for a hardcopy. 4. LPRINT USING - as in

no. 3 above.

CONTROL STATEMENTS - 1

There 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.

CONTROL STATEMENTS - 2

Example FOR-NEXT statement 120 FOR J

1 TO 50 130 K 3J1 140 PRINT J

JTAB(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 2.87CSNG(K)3

50 NEXT K

CONTROL STATEMENTS - 3

Example 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

CONTROL STATEMENTS - 4

2. GOTO statement - for unconditional transfer of

control Syntax line GOTO line

Example 120 GOTO 230 70

GOTO 10

CONTROL STATEMENTS - 5

3. IF-THEN statement Relational operators

Symbol Equal

Less than

lt Greater than

gt Less than or equal to

lt Greater than or equal to gt

These operators are used in the argument of the

IF statement to determine the flow of

control.

CONTROL STATEMENTS - 6

Compound relational operators AND , OR Simple

relational expression - involves a single

relational operator A gt 12, Blt 3. Complex

relational expression - involves several simple

relational expressions joined by the relational

operators AND and OR. Examples (Agt8) AND (Clt2)

This is true if both expressions are true

false otherwise. (Agt8) OR (Clt2) This is true

provided one or the other of the two expressions

is true false otherwise.

More in the next part..