Basic Object-Oriented Concepts

By,

Shashikant pabari

Identifiers :• They refer to the names of variables, function, array, classes

etc., created by the programmer.• Each language has its own rules for naming these identifiers.• Following are common rules for both C and C++:

oOnly alphabetic characters, digit and underscores are permitted.

o The name cannot start with a digit.oUppercase and lowercase letters are distinct.oA declared keyword cannot be used as a variable name.

Some Examples of Identifier

Identifier Validity Reason

1digit Invalid Digit at first location is not allowed

digit-1 Invalid Special characters other than underscore is not allowed

num 1 Invalid Space not allowed

num_1 Valid Underscore is valid identifier.

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Constants :

• Constants refer to fixed values that do not change during the execution of a program.• They include integers, characters, floating point number

and strings.• Literal constant do not have memory location.• Ex :

• 123 // decimal integer• 12.34 // floating point integer• “c++” // string constant• ‘A’ // character constant

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Variable :

• A variable is the name for a place in the computer’s memory where you store some data.• Declaration of variable :

• A variable can be declared right at the place of its first use.• This make the program much easier to write and reduces the errors

that may be caused by having to scan back and forth.• It also make the program easier to understand because the

variables are declared in the context of their use.• Ex :

float x; //declaration int a; //declaration

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• Reference Variable :• A new kind of variable known as the reference variable.• A reference variable provides an alternative name for a previously

define variable.• For example, If we make the variable sum a reference to the

variable total, then sum and total can be used interchangeable to represent that variable.

• Syntax : data-type & reference-name = variable-name Ex:

float total = 50; float & sum = total;

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Operators :

• An operator is a symbol that tells the compiler to perform certain mathematical or logical operation.

1. Arithmetic Operators :o Arithmetic operators are used for mathematical calculation.o Arithmetic operators are +, -, *, /, and %.

2. Relation operators :o used to compare two numbers and taking decisions based on their

relation.o Relation operators are <, <=, >, >=, ==, and != .

3. Logical operators:o Used to test more than one condition and make decisions.o Logical operators are &&, ||, and !.

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4. Assignment operators :o Used to assign the result of an expression to a variable.o Assignment operators are =, +=, -=, *=, /=, and %=.

5. Increment operators :o These are special operators in c++.o Increment operators are ++, and --.

6. Conditional operators:o A ternary operator is known as conditional operators.o Ex : x = (a>b) ? a : b; which is same as

if(a>b) x=a;else x=b;

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7. Bitwise operator :o Used to perform operators bit by bit and may not be applied to

float or double.o Bitwise operators are &, |, ^, <<, and >>.

8. Special operators :o Special operators are

& is used to determine address of the variable.* is used declare a pointer variable and to get value from it.‘ is used to link the related expression together.. is used in structure.-> is used in pointer to structure.

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9. Extraction operators (>>) :o Is used with cin to input data from keyboard.

10. Insertion operators (<<) :o Is used with cout to output data from keyboard.

11. Scope resolution operators (::) o It can be used in constructing programs. We know that the same

variable name can be used to have different meanings in different blocks.

o Ex : int m=10; { int m=20; Output : m = 20

cout << “m” << m; ::m = 10 cout << “::m” << ::m; }

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Type Casting :

• It is used to convert the type of a variable, function, object, expression or return value to another type.

• Type casting can also done using some typecast operators available in c++.

• Static_cast operator : The static_cast keyword can be used for any normal conversion between types. Conversions that rely on static (compile-time) type information.• Syntax : Static_cast <type> (object).

• Const_cast operator : The const_cast keyword can be used to remove the const or volatile property from an object.• Syntax : const_cast <type> (object).

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• Reinterpret_cast operator : The reinterpret_cast keyword is used to simply cast one type bitwise to another. Any pointer or integral type can be cast to any other with reinterpret cast, easily allowing for misuse. • Syntax : reinterpret_cast <type> (object).

• Dynamic_cast operator : The dynamic_cast keyword is used to casts a datum from one pointer or reference of a polymorphic type to another, similar to static_cast but performing a type safety check at runtime to ensure the validity of the cast.• Syntax : dynamic_cast <type> (object).

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Continue…• Example :Main(){

double a = 21.09399;float b = 10.20;int c;c = int (a);cout << “value of int(a) is :” << c << endl; c = int (b);cout << “value of int(b) is :” << c << endl;return 0;

}Output : value of int(a) is : 21

value of int(b) is : 10

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Enumerated Data Type :

• An enumerated data type is another user-defined type which provides a way for attaching names to numbers, thereby increasing comprehensibility of the code.

• The enum keyword (from c) automatically enumerates a list of words by assigning them values 0,1,2, and so on.

• This facility provides an alternative means for creative symbolic comstants.

• The syntax of an enum statement is similar to that of the struct statement.

• Ex : enum shape {circle, square, triangle}enum colour {red, blue, green, yellow}enum position {off, on}

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Control Structures

• A large number of function are used that pass messages, and process the data contained in objects.• A function is set to perform a task. when the task is

complex, many different algorithms can be designed to achieve the same goal. Some are simple to comprehend, while others are not.• The format should be such that it is easy to trace the flow of

execution of statements.• Control structure tells about the order in which the

statement are executed and helps to perform manipulative, repetitive and decision making actions.• It can be used in three ways :

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1) Sequence structure (straight line)2) Selection structure (branching)3) Loop structure (iteration or repetition)

• Basic control structures

16(a) Sequence (b) Selection (c) Loop

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• Selection Structure (Branching Statements) :• if statement.• if-else statement.• switch statement.• goto statement.• Loop structure (iteration or repetition) :• While statement.• Do-while statement.• For statement.

if Selection Structure

• Selection structure• Choose among alternative courses of action• Pseudocode example:

If student’s grade is greater than or equal to 60Print “Passed”

• If the condition is true• Print statement executed, program continues to next

statement• If the condition is false

• Print statement ignored, program continues• Indenting makes programs easier to read

• C++ ignores whitespace characters (tabs, spaces, etc.)

• Translation into C++If student’s grade is greater than or equal to 60

Print “Passed”

if ( grade >= 60 ) cout << "Passed";

• if structure • Single-entry/single-exit

true

false

grade >= 60 print “Passed”

if/else Selection Structure• if

• Performs action if condition true• if/else

• Different actions if conditions true or false• Pseudocode

if student’s grade is greater than or equal to 60print “Passed”

elseprint “Failed”

• C++ codeif ( grade >= 60 ) cout << "Passed";else cout << "Failed";

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Example

if ( grade >= 90 ) // 90 and above cout << "A";else if ( grade >= 80 ) // 80-89 cout << "B";else if ( grade >= 70 ) // 70-79 cout << "C"; else if ( grade >= 60 ) // 60-69 cout << "D";else // less than 60 cout << "F";

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Switch Case• switch

• Test variable for multiple values• Series of case labels and optional default case

switch ( variable ) {case value1: // taken if variable == value1

statements

break; // necessary to exit switch

case value2:

case value3: // taken if variable == value2 or == value3

statements

break;

default: // taken if variable matches no other cases

statements break;

}

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While loop

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sample <= 2000 sample = 2 * sampletrue

false

• Flowchart of while loop

While loop

• Repetition structure• Action repeated while some condition remains true• Psuedocode

while there are more items on my shopping list Purchase next item and cross it off my list

• while loop repeated until condition becomes false

• Exampleint sample = 2;while (sample <= 2000 ) sample = 2 * sample;

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for loop• General format when using for loops

for ( initialization; LoopCount ;increment/decrement )

• Examplefor( int sample = 1; sample <= 10; sample++ )

cout << sample << endl;

• Prints int value from one to ten

 

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