QBASIC Programming-Elements, Features, Statements. Learn QBASIC within few minutes...

QBASIC is a high level computer language published by Microsoft which stands for Quick Beginners All Purpose Symbolic Instruction Code. QBASIC environment includes a full screen syntax checking, multi-file and multi-window editing, full debugging facilities, pull-down menus, syntax-checking editor and a simple yet a powerful menu structure that can be driven through either by a keyboard or a mouse. Once you are in the QBASIC
environment you can edit, run, debug and rerun the program without switching programs.

Features

Some of the salient features of QBASIC are as follows:

1.   Simplified grammar.

2.   Dynamic program debugging.

3.   Facility for manipulation of strings.

4.   Easy to learn and understand.

5.   Provides clear and friendly error messages.

Elements of QBASIC Programming

The important elements of QBASIC program are:

1. QBASIC character set

Character set is a defined list of characters recognized by QBASIC program. A character represents any letter, digit or any other sign. The QBASIC has the following character set:

Alphabets              :   A to Z (small and capital letters)

Numbers                :   0 to 9

Special characters  :   ; = + - * / ^ ( ) % $ # ! , . ‘ “ : & ? \

2. Keywords (Reserved words)

Keywords are the words that convey a special meaning to the language. These are reserved for special purpose and must not be used as normal identifier names. Some of the keywords are: REM, CLS, INPUT, LET, PRINT and END.

3. Variables

Variable is an area in the computer memory and within a program that can be referred to by name and whose value can be altered during program execution. It also provides a way of labeling data with a descriptive name, so our programs can be understood more clearly by the reader and ourselves. It is helpful to think of variables as containers that hold information. Their sole purpose is to label and store data in memory. Variables are of two types: numeric variable and string variable.

a) Numeric Variable: Numeric variable has a number as its value. It must begin with an alphabet and the remaining characters, if used, may be alphabets or digits or both. Numeric variables may be declared as:

i) Integers and long integers Variable

Integer variable is declared by using a percent sign (%) as the last character of the variable name. Integers are stored as 2 bytes ranging in value from -32768 to +32767. Long integer variable is declared by using an ampersand sign (&) as the last character of the variable name. Integers are stored as 4 bytes ranging in value from -2147483648 to +2147483647.

ii) Single Precision Variable

Single precision variable is declared by using an exclamation sign (!) as the last character of the variable name.

iii) Double  Precision Variable

Double precision variable is declared by using a number sign (#) as the last character of the variable name.  

  

b) String Variable

String variable represents numbers, alphabets and special characters. This variable should :

• Begin with an alphabet.
• End with dollar sign ($).
• Be of more than one characters and numbers but no special characters are allowed.

String variable are of two types:

a) Variable-length string

A string by default is of variable length, which means that the size of the variable changes when the length of the allotted string changes. Variable length strings are very flexible.

b) Fixed-length String

Compared to variable length strings, fixed-length strings are rigid. After their length is declared, it does not change. If you attempt to store more text than its capacity completely, the text gets trimmed from the right.

4. Constants

Constant is a value that cannot be altered by the program during normal execution, i.e., the value is constant. Constants are of two types: numeric constant and string constant.

a) Numeric constant

As the name suggests, numeric constant contain numbers. It is a positive or negative number on which mathematical operations such as addition, subtraction, multiplication, division, etc.

b) String constant

String constant contains alphanumeric characters enclosed in double quotation marks.

5. Operators and Expressions

An operator is a symbol representing the operations they perform on operands in a program. The values on which the operators work are referred to as operands.

An expression is a programming statement that has a value. It is composed of operators and operands. An operand may be a variable or a constant.

There are 4 types of operators. They are:

a) Arithmetic Operators

Arithmetic operators are used to perform operations such as addition, subtraction, division, multiplication, negation and exponentiation.

b) Relational Operators

Relational operators are used to evaluate and compare two values of the same type, either both numeric or both string. The result of comparison is either TRUE or FALSE.

c) Logical Operators

Logical operators are used to connect two or more relations (expressions that contain relational operators) and return a true or false value, which is used to make decisions regarding program flow.

d) Concatenation Operators

Concatenation operators join multiple strings into a single string. QBASIC use the plus sign (+) as a string concatenation operator.

QBASIC Statements

QBASIC Statement is an instruction given to the computer to carry out an action. The statements can be divided into four categories:

i.     Declaration Statement

ii.    Assignment Statement

iii.   Input/output Statement

iv.  Control Statement

REM Statement

The word REM stands for REMarks. It is used to write comments in the body of the program. REM is a non-executable statement. The general format of REM is:

REM <remark>

Or

<remark>

CLS Statement

The CLS statement is used to clear the screen and it leaves the cursor at the top left corner of the screen. The general format of CLS is:

CLS

LET Statement

The LET statement is an assignment statement. It is used to assign the value of an expression to a variable. LET is an optional keyword. The general format of LET is:

LET <variable> = < expression >  

INPUT Statement

INPUT statement is used to receive data items from the keyboard during program execution. The general format of INPUT is:

INPUT [“definer”;] list of variables

READ…DATA Statement

The READ…DATA statement contains the names of the memory locations to be used to store the information in. They are used in the following form:

READ [variable 1, variable2,… ]

…      

…

DATA [constant 1, constant2,…]

CONST Statement    

CONST statement is a non-executable statement that declares symbolic constants to be used in place of numeric or string values. The general format of CONST is:

CONST constantname =  expression [, constantname = expression]

PRINT Statement

The PRINT statement is used to display numeric or string data on the screen. A question mark (?) may be used instead of the word PRINT. The general format of PRINT is:

PRINT [List of expressions] [, \ ;]

Or

? [List of expressions] [, \ ;]

LOCATE Statement

The LOCATE statement is used to move the cursor to the specified position on the screen and determine the height of the cursor. The general format of LOCATE is:

LOCATE [row][,[cursor][,[start][,stop]]]]

                                                   

END Statement

The END statement tells the computer that the program is over, and should stop reading lines. . The general format of END is:

END