Contents Introduction Names Variables The Concept of Binding Type Checking Strong Typing Type Equivalence Scope Scope and Lifetime Referencing Environments Named Constants Introduction

Contents

• Introduction
• Names
• Variables
• The Concept of Binding
• Type Checking
• Strong Typing
• Type Equivalence
• Scope
• Scope and Lifetime
• Referencing Environments
• Named Constants

Introduction

• Imperative programming languages are abstractions of von Neumann computer architecture
• Memory: stores both instruction and data
• Processor: provides operations modifying the contents of the memory.
• Variables are the abstraction of memory cells
• Variables are characterized by attributes
• To design a type, must consider scope, lifetime, type checking, initialization, and type compatibility

(1) limited such as (a) COBOL: maximum 30

(b) FORTRAN 90 : maximum 31

(2) Unlimited such as Ada, C#, and JAVA

Names

A Name is a string of characters used to indentify some entity in a program.

(Ex. variables, formal paramètres, methodes, etc.)

Names

Length

Case Sensitivity

Relation with special character and reserved words

• Meaning: distinguish between capital letters and small letters.
• Types: some languages are

(1) case sensitive such as C, and Java

2) not case sensitive such as Ada, and Pascal.



• Disadvantage of case sensitivity:
• readability (names that look alike are different)

• Meaning: A reserved word is a special word that cannot be used as a

user- defined name.

• Example: RW in Java: if, for, while, return,…..
• Disadvantage: if the language contains large number of RW then

many collisions occur.

(e.g., COBOL has 300 reserved words!)



Special Characters(SC)

• Meaning: Other than letters and digits.
• Example: In some languages, we use the SC in the name.

(1) PHP: all variable names must begin with $.

(2) Perl: all variable names begin with special characters, which

specify the variable’s type.

• Meaning: A keyword is a word that is special only in certain contexts,
• Example: In Fortran,
• Real VarName (Real is a data type followed with a name,

therefore Real is a keyword).

• Real = 3.4 (Real is a variable).

Variables

• Meaning: A variable is a named location in memory that is used to hold a value that can be modified by the program.

• Attributes:

• Name : not all variables have them.