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Introduction to QBASIC

Govind Prasad Joshi February 04, 2022 ,Introduction of QBASIC ,QBASIC

Introduction to QBASIC

Introduction

QBASIC (QUICK BASIC) is a programming language developed by Microsoft Corporation to use in the MS-DOS operating system. It is the successor of the earlier version of BASIC. QBASIC was developed by John J. Kemeny and Thomos E Kurtz in 1964 at Dartmouth College, New Hampshire. Today many version of BASIC are available such as BASICA, GWBASIC, Turbo BASIC, VB, and QBASIC etc.

QBASIC interpreter is a simple many driven program that is mostly used to make programs by beginners but it can be sued to write very complex and useful programs. It is a full screen editor that checks syntax error. It has pull down menus with full debugging facilities. It is very user-friendly language which helps to develop customized software packages for business application music and games.

Features of QBASIC

i) It is easy to learn and understand.

ii) It is user friendly language.

iii) It is portable.

iv) It allows us to test/debug the program.

v) It checks automatically syntax errors.

vi) It provides online help.

vii) It supports structure programming.

viii) It allows functions or procedure to be defined in the program.

Elements of QBASIC

Elements of QBASIC are the main building block of QBASIC program. the elements of QBASIC are necessary to build or write program in QBASIC. Following are the elements of QBASIC:

i) Character Set

ii) QBASIC words

iii) Constants

iv) Variables

v) Operators

vi) Expression

Character Set

QBASIC contains three sets of characters. The character set includes alphabet, number and special characters. Special symbols, sign other than alphabets and numbers are called special characters.

Category	Character/symbol
Alphabet	A to Z or a to z
Numerical/digits	0 to 9
Special characters	$,%,@,!,(,_,),?, \, / etc..

QBASIC words

The words which are used in QBASIC are called QBASIC words. Following are the two types of QBASIC words:

i) Reserved words (keywords)

ii) User defined words

Reserved words (Keywords)

The reserved words are also called keywords which have special meaning to the QBASIC. Keywords are program, independent and provide the same meaning in different programs. Examples: CLS, INPUT, PRINT, LET, SQR etc..

User Define Words:

The words which are defined by the user according to his need is known as User define words. The word does not have any specific meaning. In each and every program user define has the different meaning.

Constants

The entity (data or value) which cannot be changed during the program execution is called constant.

Types of constants:

a) Literal Constant

i) Numeric constant

ii) String constant

b) Symbolic constant

Numeric Constant:

All the numeric values or data are known as numeric constants. Numeric constants are numbers having positive or negative values on which mathematical operation such as addition, subtraction, multiplication, and division could be solved. Examples: LET x=450, LET p=34.65 etc.

Rules to be followed while writing numeric constants:

i) Number with comma is not allowed.

ii) A number can be preceded by positive or negative sign. Negative sing (-) is compulsory but positive (+) is optional.

iii) No special character is allowed with number except decimal point.

String Constant:

String constant is a text value that consists of alphabets, digits, symbols and special characters, written within double quotation marks.

It cannot use in mathematical calculations. Two strings can be concatenated or joined. Example: LET a$= “AVN”, LET p$= “4021” LET m$= “%$#@!” etc.

Symbolic Constant:

A scientific symbol which is used to represent the fixed value is known as Symbolic constant.

Syntax:

CONST constant name=expression

Example:

CONST pi=3.1416

Note: Here, the value of pi cannot be changed or modified during the time of program execution.

Variable

Variable is an entity whose value changes during the program execution. It represents the storage location in computer’s memory.

Rules of Variable naming:

i) All the variable name should be start with alphabet.

ii) It can have numbers, period(.), and data type declaration characters such as (%,!,#) as suffix.

iii) A variable name can have maximum of 40 characters.

iv) Blanks spaces are not allowed in verifiable name.

v) QBASIC keywords (LET, PRINT, INPUT, CLS etc) are not allowed as variable name.

vi) No special characters such as [,],*,~ etc. are used as variable name.

vii) A variable name cannot begin with FN unless its function is defined.

Types of Variable:

Following are the different types of variables.

i) Numeric variables

ii) String variables

Numeric Variable:

Numeric variable is the variable that stores numeric data including whole number and the number with decimal. Numeric variable does not store string data.

Example: a, a%, a&

String Variable:

A variable which stores letters, numbers, and other special characters is known as string variable. A string variable begins with alphabet and ends with dollar ($) sign. Example: m$, a34$ etc.

Declaration of Variables

In most programming language, variables must be declared in advance for the compiler. One of the most popular features of BASIC was that it didn’t force the programmer to declare all variables in advance. In QBASIC variable can be declared in following two ways.

Implicit Declaration:

In implicit variable declaration, the type of variable declared at the same time when the value is assigned to it. It is specially used in simple variable. The variable type is declared by using data type declaration characters which are always used as suffix in variable name such as ($,%,! and #).

Example: a%=45678.56

Note: Here variable has been declared as an integer variable and the value is assign as 45678.56

Example: m$= “Dhangadhi”

Note: Here, m$ declared as a string variable to store Dhangadhi string. Here, declaration and assignment is done at the same place.

Explicit Declaration:

A variable declaration that can be declared before they are used in a program without any data type suffix is known as explicit declaration. it is generally done at the beginning of the program. A variable is declared explicitly using DIM statement. This type of declaration does not assign the value but informs the program about variables.

Syntax:

DIM variable name AS TYPE

Variable: Any valid variable names

Type: defines the types of variables (numeric and string) it can be INTEGER, LONG, SINGLE DOUBLE, STRING

Example:

DIM marks AS INTEGER

Here, Marks is declared as an integer variable explicitly

DIM name AS STRING

Here, name is declared as string variable explicitly.

Date Types

The information such as name, age, date, salary, marks, etc. is called data. Each data can store by a variable with same type. The choice of data types for your variables can make a difference in the results of the calculations. The proper variable types are determined by the nature of the values they represent. The choice of data types is frequently increase speed of execution. The varieties of such information it is classified in different groups. Such data types used in QBASIC are given by:

a) String Data Types

i) Variable Length String

ii) Fixed Length String

b) Numeric Data Types

i) Integer

ii) Long integer

iii) Single Precision

iv) Double Precision

a) String Data Types

A string is a combination of characters and they are real objects, and hence, it is possible to concatenate, modify and test them.

The string data type is a combination of alphanumeric characters which are enclosed by double quotation mark and assign to string variable. Data range of string variable is 0 to 32767 characters and memory consumption is 4 bytes. There are two types’ string data types. They are given below:

i) Variable length string

Any text or alphanumeric value which can be input from or enclosed by double quotation mark is called variable length string.

Example:

LET N$ = “Class 9”

INPUT “Enter your name: “ ; N$

DIM Nam AS STRING

In the given example N$ is a variable length variable which do not have any fixed character length and can be declare or use wherever we need in the program. The variable N$ may store any string value with different length. Such variable declaration is called implicit declaration.

ii) Fixed length string

A fixed length string is also text or alphanumeric value which length is specified by the corresponding variable.

Example:

DIM Nam AS STRING * 15

DIM Address AS STRING * 30

In the given example Name and Address are the fixed length string variable. The variable Name and Address can store only 15 and 30 characters respectively. Fixed length string variable most declare before use with specified no of characters length. This is an explicit variable declaration.

The Name variable can store maximum 15 characters. In case of fewer characters it keeps blank spaces to consume given number of characters. If you supply the name “Ram Singh” it contains with 6 blank spaces.

b. Numeric Data Types

Numeric data types are any numeric values either positive or negative. There are four different types of numeric data types in QBASIC. They are given below:

i) Integer

Integer data type is a positive or negative number which does not contains decimal point. Or the number without decimal point is called integer data type.

Integer variables are used to assign the integer data types. Integer variable name used % sign with name of the variable. The range for integer variable is from -32768 to 32767 and memory consumption 2 bytes.

Example: LET age% = 15

ii) Long integer

Integer data type has very short range so that long integer data type is used to store such of the large numbers. Long integer data stored to the variable which used & sign with the name. Its range is from -2147483648 to 2147483647 and memory consumption 4 bytes.

Example:

LET n& = 123454321

iii) Single Precision:

A single precision variable can store floating point number up to six digits after the decimal point. If the number contains 7 digits, it is rounded to the closed value. The single precision variable is declared using exclamation (!) symbol at the end of the variable name. It occupies 4 bytes of storage space in the memory.

Example:

per!, interest! etc.

iv) Double Precision:

The double precision variable holds numbers having decimal point up to 16 digits. It is declared using hash (#) symbol at the end of the variable name. It stores numeric data occupying 8 bytes of memory space.

Example:

total#, gross# etc.

Data type Identifier

Data type declaration characters are known as data type identifier symbols. Following are the symbols which are used as data type identifier.

Data type	Symbol	Maximum	Minimum	Bytes used
Integer	%	32767	-32768	2
Long integer	&	2,147,483,647	-2,147,483,648	4
Single precision	!	3.402823E+38	1.401298E-45	4
Double precision	#	1.7976931D+308	4.940656D-324	8
String	$	32767	0	2

Expression

An expression can be a string or numeric constant, a variable or single value obtained by combining constants, variables and expression. Following are the different types of expression supported by QBASIC.

a) Arithmetic Expression:

An expression, which contains values, variables and operators that return a single numeric value after operations is called arithmetic expression.

Example: LET s=5+8-a

b) Logical Operations:

A logical expression contains values and operations, which are evaluated by QBASIC and returns one of two logical values (1 or 0) or (True or False)

Example: PRINT 2>7

In above expression it returns false value that is 0 because 2 is not greater than 7.

c) String Expression:

An expression, which returns string value after processing string with the help of string operator, is called string expressing.

Example: PRINT m$+n$

N above example it display the string value on the screen combining the string values of variables m$ and n$

Operators

An operator is a symbol or sign used to indicate a specific operation between the operands in a program. Operators are special symbols that are used in expression, which indicates an operation and performs mathematical calculation, comparison, or logical operations. An operand is something on which the operator acts on. The operands are variable or constants. The operator tells what operation to be performed between the operands.

x + y

In the above example the Plus (+) is an operator that tells the addition operation to be performed between the operands x and y.

The different types of operators that support QBASIC are given by:

i) Mathematical operators:

The mathematical operators are the arithmetical operators used to perform normal mathematical calculations such as addition, subtraction, multiplication and division. QBASIC does calculation according to the normal rules of mathematics.

The different symbols are used as mathematical operator with their use is given below.

Operator	Operation	Example
+	Addition	10 + 3 = 13
-	Subtraction	10 – 3 = 7
*	Multiplication	10 * 3 = 30
/	Division	10 / 3 = 3.333
\	Integer Division	10 \ 3 = 3
^	Exponential / Power	10 ^ 3 = 1000
MOD	Modulus Division	10 MOD 3 = 1

Conversion of algebraic expression to BASIC expression

All of the mathematical expressions cannot write directly in BASIC so that we have to change such notations into BASIC notations. In the table given below shows the rules of conversion of algebraic expressions into BASIC expressions and vice-versa.

Order of preference

As we already discussed, QBasic does calculation according to the normal rules of mathematics (algebra). The order of preference of mathematical operators is given below;

Order of operator	operation	Example
^	Exponentiation or power	2^4=16
* or /	Multiplication or Real Division	2*4=8 / 5/2=2.5
\	Integer division	5\2=2
MOD	Modulus (Remainder)	5 MOD 2 = 1
+ or -	Addition or Subtraction	5+2=7 / 5-2=3

ii) Relational Operators:

Relational operators are used to compare values between two variables, constant or arithmetic expression. The result of comparison is either “true” of “false”

The different symbols are used as relational operator with their use is given below.

Operator	Relation	Numeric	String
>	Greater than	A > B	A$>B$
<	Less than	A < B	A$<B$
> =	Greater than and equal to	A > = B	A$>=B$
< =	Less than and equal to	A < = B	A$<=B$
=	Equal to	A = B	A$=B$
<>	Not equal to	A <> B	A$<>B$

iii) String / Concatenation operator ( + )

A string expression consists of string constants, string variables, and other string expressions combined by string operator (+).

When a “+” sign used between two different strings, it is said to be string or concatenation operator. This operator does not add the string values but brings together so that it seems a single word.

Example:

A$ = “Raja”

B$ = “Ram”

C$ = A$ + B$

Now value of C$ will be “RajaRam”

iv) Logical operators

Logical operators are used in decision making. They combine two or more relational expressions to evaluate a single value i.e. true or false. QBASIC support six logical operators (AND, OR, NOT, XOR, IMP & EOQ) among them first three are commonly used.

Operator	Meaning
AND	Provides true result when all the expressions become true.
OR	Provides true result when at least one of the expressions become true
NOT	Provides reverse result

A truth table is a table showing the necessary inputs and corresponding output values from the input values. The truth table is used to calculate the output from the supplied input. Following truth table makes clear about logical operators.

AND truth table