Variables – DataTypes & Expressions In PHP

VARIABLES AND EXPRESSIONS

• A variable is a named memory location.
• A variable stores different types of data
• A variable contains data that keep on changing during execution.

An expression is a combination of:

• Variables
• Constants
• Functions
• Operators

IDENTIFIERS IN PHP

Are names given to various elements of a program such as variables, constants, arrays, functions, and classes

Rules to be followed while naming identifiers are as follows:

• It must begin with a letter
• It must contain only letters (A to Z) or digits (0-9)
• It must not have any special characters including blank space
• An underscore (_) character can be used to add space in the identifier to make it more readable
• Valid identifiers names are firstnum, lname, net_sal, add8num, and NewNum

VARIABLES AND DATA TYPES

• Variable is an identifier whose value keeps changing throughout the execution of a program
• Variable has:
  • Name – refers to the variable
  • Data type – refers to the type of data that the variable can store
• Variables are used to store:
  • User information
  • Intermediate data such as calculated results
  • Values returned by the functions

Rules to be followed for a variable are as follows

• A variable is of the same data type as the value stored in it
• Variable name is preceded by a dollar sign ($) and can only contain alpha-numeric characters and underscores
• Value to the variable is assigned with the equal to (=) operator, with the variable on the left side and the expression on the right side
• A variable created without any value assigned to it, takes the default value of NULL
• A variable is case-sensitive

PHP supports primitive data types that are categorized as follows:

• Scalar Types
  • Integer
  • Float
  • String
  • Boolean
• Compound Types
  • Array
  • Object
• Special Types
  • Resource
  • Null
• Constants

PHP is a Loosely Typed Language

• PHP automatically converts the variable to the correct data type, depending on its value.
• In other languages such as C, C++, and Java, the programmer must declare the name and type of the variable before using it.

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