C++ Basics : Program structure, namespace, identifiers, variables, constants, enum, operators, typecasting, control structures

1. Basic Object-
Oriented Concepts
By,
Shashikant pabari

2. 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++:
o Only alphabetic characters, digit and underscores are
permitted.
o The name cannot start with a digit.
o Uppercase and lowercase letters are distinct.
o A declared keyword cannot be used as a variable name.

3. 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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4. 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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5. 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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6. Continue…
• 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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7. 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 %.
1. Relation operators :
o used to compare two numbers and taking decisions based on their
relation.
o Relation operators are <, <=, >, >=, ==, and != .
1. Logical operators:
o Used to test more than one condition and make decisions.
o Logical operators are &&, ||, and !.
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8. Continue…
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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11. 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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12. Continue…
• 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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13. 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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14. 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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15. 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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16. Continue…
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

17. Continue…
• 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.

18. if Selection Structure
• Selection structure
• Choose among alternative courses of action
• Pseudocode example:
If student’s grade is greater than or equal to 60
Print “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.)

19. • 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”

20. 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 60
print “Passed”
else
print “Failed”
• C++ code
if ( grade >= 60 )
cout << "Passed";
else
cout << "Failed";
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21. 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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22. 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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23. While loop
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sample <= 2000 sample = 2 * sample
true
false
• Flowchart of while loop

24. 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
• Example
int sample = 2;
while (sample <= 2000 )
sample = 2 * sample;
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25. 25
for loop
• General format when using for loops
for ( initialization; LoopCount ;increment/decrement )
• Example
for( int sample = 1; sample <= 10; sample++ )
cout << sample << endl;
• Prints int value from one to ten

26. The End
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