Elements of QBASIC programming

To construct the QBASIC program, we have to arrange some standard elements.The elements used in Qbasic are as follows:

• Character set
• Variables
• Constants
• Operator and Operands
• Expression
• Statements

Character Set

QBASIC has the character set consisting of the following elements:

1. Alphabets: A, B, C,....Z
2. Digits: 0, 1, 2........,9 and
3. Special characters: + - * / ( ) . , $ ; ,: ,= ,> ,< , ^

The symbol ^ (caret) is used to denote exponentiation operator, the symbol * (asterisk) is used to denote multiplication and other symbols; have their usual meanings.

Constants

A quantity in a computer program which does not change its value during the execution of the program is called a constant. QBASIC allows the following constants:

• Numeric constant

  The numeric constant is one that is formed by a sequence of digits 0, 1, 2,.....9 and may include a decimal point. A numeric constant may be an integer or a real number. 383, +57, 0, -6.2 and 6.15E4 are valid numeric constants. The number 6.15E4, in fact, represent 6.15 * 104. The notation E is used to represent the exponential form. The number after E is the exponent which can be positive or negative. However, its length cannot exceed two digits.

  It is also important to keep in mind that:

  • QBASIC does not distinguish between an integer and fraction.
  • Commands are not allowed in a numeric constant.
  • The limit on the number of digits that can be used varies from computer to computer. Normally, a numeric constant can have up to a maximum of eight digits.

• String constant

  A string constant consists of a sequence of characters which must be enclosed by a quotation mark.

Variables

The quantity which may change its values during the execution of the program is called the variable.

In QBASIC, variables are also of two types:

• Numeric variable: Numeric variable can assume numeric value and is represented by an alphabet or an alphabet followed by another alphabet or digit. For example A, C, A2, ABC, A6 etc, represent numeric variables.
• String variable: A string variable is represented by an alphabet followed by dollar ($) sign. It should be kept in mind that while constructing the string variable, dollar ($) should be the last character. For example, B1$, NAME$, BOOK1$, etc are valid string variables.

Expression

Operands

Operators

Statements