Elements of QBASIC

Elements of QBASIC language are:

  1. Character Set
  2. Constants
  3. Variables
  4. Operators
  5. Expressions

1.Character Set: The set of valid characters that a language can be recognize. A character include alphabets, numbers and special characters.

2. Constants: The data items that never change their value during the execution of a program. There are two types of constants:- Numeric and String.

-Numeric Constants: They are positive or negative numbers on which addition, subtraction, multiplication and division can be performed and they do not contain commas(,). Eg:450, -742

– String Constants: They are a set of alphanumeric or special characters which is enclosed with double quote(“) Eg: “I live in Kathmandu”, “Roll no: 007” etc

3. Variables:  It is the storage area whose contents can vary during the processing of the program.  A variable represent a value in a program. A value of program can be changed during the execution of program.

properties of Variables: 

  • Any variable name can be up to 40 characters long.
  • A variable name can have alphabets, numbers and decimal but cannot be kept reserved words.
  • Variable name must be begin with a letter but not with fn or FN as it represents function call. eg: “fnname”.

There are two types of variable:

-Numeric Variable: It stores only numeric values. It is declared as:

Integer and long integers: Integer value is declared by  using percent sign(%) as the last character of the variable name. It is stored as 2 bytes ranging from -32768 to +32767 and Long integer is declared by using ampersand sign (&), it is stored in 4 bytes ranging in values from -2,147,483,648 to +2,147,483,647

Single precision variable: It is declared by using  an exclamation (!) sign. It is default numeric value and it can be used without declaration sign. Eg: MarksOfComputer!, SumOfTwoNumbers! etc.

Double precision variable: It is declared by using hash(#) sign. It can also store number with decimal points. Eg: KathmanduJhapaDistance#, CapitalOfProvinceOne# etc.

-String Variable: It stores a string constant or alphanumeric data, the last character of a string must be dollar sign($). Eg: LET Name$=”Nepal”, LET DOB$=”1989″ etc

4. Operators: They are the symbols that performs operations on the operands. It refers to be a symbol which represents what type of operations has to be performed.

-Arithmetic Operators: It performs mathematical calculation like addition, subtraction, multiplication and division, MOD represents modular division.

– Relational Operators: It is used to perform more than two values of same type either numeric or string. The result of the operation may be either True or False. Eg: =,  >,  <,  >=,  <=,  <>.

-Logical Operators: It combines the result of two or more than two relational operators as a singles and gives either TRUE or FALSE. Eg: AND, OR, NOT.

AND represents multiplication of two numbers.

OR represents addition of two numbers

NOT represents just opposite to each other i.e it returns TRUE if the result is FALSE.

-String Operator: It joins more than two string data, plus(+) sign is used. The action of combining two string is called concatenation. Eg: “Roll No” and “007” results as “Roll No 007”.

5. Expressions:  It is the combination of operators, constants and variables that evaluated to get a result.

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