Variables

A variable refers to a position or location in the memory of the computer where a value can be stored.

Initially – dose not need a value

The word variable indicates that the value of the variable may vary as needed or processing is done.

 Naming a variable

Every variable is given one exact name (Descriptive Name)

Rules for naming variables

1: Each must have a unique name

2: Each must have a descriptive name

3: Cannot contain spaces (words can be joined to form a name: bookPages or book_pages)

4: Cannot contain only numbers

5: Names must start with a letter

6: Name cannot contain special characters

7: Must be short and descriptive as possible

How to name a variable

Convention is to use only lover-case letters in the name of a variable. Except where two or more words are joined. In such cases all the following words start with upper-case which is known as camel casing.

Description   Name  
Name of employee empName
Price of car carPrice  
Author of book author  
Quantity in stock quantity  
Age of student stAge  
Total number of sales totNumSales

 Types of variables

The following data types are applicable when variables are classified

2.1.1    Numeric variables

 

Interger variable

Whole numbers (no fractional or decimal)

Example:       15     -2334         9728       0

 

Real number variable

Contains decimal point

Example:   12.47       -987.121       17.00

 

2.1.2    None – numeric variables

 

Character variable

Single letter, number or special character (Always enclosed in quotes)

Example:       “A”       “G”       “*”         “8”

The character “8” which is declared as a character is not regarded as a numeric and may not be used in calculations. When declared as a character, it can be used as a code – for instance, the group number is “8”

String variable

Two or more character (must be enclosed in quotes)

Example:   “32 Long Street”

Or a message, such as “The name is found”

 

Boolean variable

Can only contain a true or false value.

In a computer language, a true value is represented by a no-zero value, whereas a false value is represented by a zero.

A Boolean variable is used to test if a specific condition is true or false. (Also called a logical variable)

Example: Is the person a club member?   True or False

 The value of a variable

A variable need not contain an initial value. A value can be assigned to a variable according to its data type.

For instance – The variable costPrice must contain a numeric real value.

A value can be assigned to a variable while the statements in the algorithm are being processed.

 

Rule: When the value of a variable changes the previous value of the variable is replaced by the new variable

Constants

 

Use same rules as variables but have:

Fixed Value

Value cannot change

Constants are used where we know the value will never vary during the execution of the program.

(Can be any type of Data)

 

Example:  

There is always 24 hours in a day.

 

4: Using variables in expressions and assignments

 

The assignment symbol (=) is used to assign an initial value or an expression to a variable.

 

Syntax: Variablename = Value    
  or  
  Varaiblename = Expression  
         
Example: totalNumStudents = 20  
  totalNumStudents = numMales + numFemales

The example, totalNumStudents = 20, means that a variable that contains the total number of students is equal to 20.

The second example, however indicates that the total number of students is equal to the number of male students plus the number of female students. numMales and numFemales are both names of variables.

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