Transcript GWBASIC PROGRAMMING - Faculty of Engineering

Building blocks No. 2
and
GWBASIC PROGRAMMING
– For new comers,GWBASIC a good starteasy 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 : 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<=2 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,
-3.45E+12, 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
-32768< x < 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) < x < 10^(+38)
(^ refers to exponentiation, meaning raised to)
Example 234.567, -9.8765, 6.023E+23
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
1. Integer
2. Single precision
%
!
EXAMPLE
3%, 564%
1.34! , 43.7865!,
23.56E-8
3. Double precision
#
3.4567#, 2.67D+21
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
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 are
initialized to 0.
2. VARIABLES - 3
VARIABLE DECLARATION
1. Each variable must be assigned a type.
2. 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.
3. Explicit variable type declaration can be
accomplished using either the type declaration tags
(%.!,#,$) or the DEFtype statements.
2. VARIABLES - 4
EXAMPLES – EXPLICIT VARIABLE TYPE
DECLARATION
1. Using the tag characters – A%, ITEM$, Y!, BBC#
2. 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 twodimensional 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)
Note:Put DIM statements at the beginning of the
program.
3. OPERATIONS - 1
1. 1. Hierarchy of operations: list is of descending
priority
2.
Operation
Symbol
Exponentiation
^
Example
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
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
3.6*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 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 >= 0
6. Exponential
EXP(X)
7. Natural logarithm
LOG(X) , X > 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
but keep its sign
SGN(X)
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
constant
CDBL(X)
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);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.
CONTROL STATEMENTS - 1
There are four control statements in Gwbasic: FORNEXT, 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 = 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%
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
<
Greater than
>
Less than or equal to
<=
Greater than or equal to >=
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 > 12, B<= 3.
Complex relational expression - involves several simple
relational expressions joined by the relational operators
AND and OR.
Examples:
(A>8) AND (C<2) This is true if both expressions are
true; false otherwise.
(A>8) OR (C<2)
This is true provided one or the
other of the two expressions is true; false otherwise.
More in the next part…..