Variable Declaration and Initialization, Chapter3 - Object Oriented Programming in C plus plus

Computer Science SLO Based Key Point Notes

👉👉👉 Computer Science 12th Class Notes (Main Page)

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Unit 3: Object-Oriented Programming in C++

3.2.5 Variable Declaration and Initialization

Variable Declaration

• The process of specifying the variable name and its data type is called variable declaration.
• C++ is a typed language which means that all variables must be declared before they are used in the program.
• C++ compiler will give an error if an undeclared variable is used in a program.

The general syntax to declare a variable is:

                                                data_type    variables;

where “type” specifies the data type of variable which may be int, float, double, char, etc. “variables” specify the list of variable names of the same data type separated by commas.

Example:
                                                    int sum;

The above declaration statement tells the compiler that the variable name is “sum” and its data type is “int”.

A list of variables of the same data type can be declared in a single declaration statement i.e.
                                            float a, b, c, d, e;

Variable Initialization

• The process of assigning a value to a variable at the time of declaration is known as variable initialization.
• The equal sign “=“ is used to initialize a variable.
• When a variable is declared, the compiler allocates memory location which contains some data that is meaningless for the program. It is known as garbage value which may produce unexpected results.
• All variables should be initialized to avoid this problem.
• The syntax of initializing a variable is as follows:

                                    Data_type variable_name = value;

Example:
                int n = 100;
                float average = 34.55;

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3.1 Introduction to Object-Oriented Programming (OOP):

3.1.1 Computer Program/Software:

3.1.2 Header File and Reserved Words

3.1.3 Structure of C++ Program

3.1.4 C++ program statement Terminator:

3.1.5 Comment statement in C++ Program:

3.2.1 C++ Constants and Variables

3.2.2 Rules for Naming a Variable:

3.2.3 Different C++ data types for variable

3.2.4 The Constant Qualifier (const)

3.2.5 Variable Declaration and Initialization

3.2.6 Type Casting

3.3: Input / Output Handling

3.3.1 The cout Statement

3.3.2 The cin Statement:

3.3.3 The getch() function:

3.3.4 Commonly Used Escape Sequences

3.3.5 Commonly Used Escape Sequences

3.3.6 The Programing with I/O Handling Function

3.3.7 The Manipulators endl and setw

3.4.1 Types of Operator in C++:

3.4.2 UNARY, BINARY AND TERNARY OPERATORS

3.4.3 Order of Precedence of Operator

3.4.4 Expression in C++

4.1.4. The Switch Statement:

Chapter 3 (Complete Key Point Notes)

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👉👉👉 Computer Science 12th Class Notes (Main Page)

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(National Book Foundation - As Federal Textbook Board, Islamabad 

Based on National Curriculum Pakistan 2026-2027 and Onward prescribed by Federal Board of Intermediate and Secondary Education, Islamabad, and All Pakistan Boards) 

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