3/3/20

Elements of C++ language


Elements of C++ language

Tokens and Identifiers: Character Set and Symbols, Keywords, C++ Identifiers

 Variables and Constants: Integers & Characters, Constants and Symbolic constants, Dynamic initialization of variables, reference variables, enumerated variables

Data Types: Basic data types, arrays and strings, user defined data types

 Operators: Arithmetic, relational operators and operator’s precedence, logical operators, manipulators, type conversions and type cast operators

Console I/O: cin, cout functions

 Control Statements: The if statement, if-else; else ... if switch statements

Loops: for and do-While statements, Break, continue, go to

Tokens and Identifiers: Character Set and Symbols, Keywords, C++ Identifiers

Character set and symbols: -
1.   Combination of English language i.e. alphabets and white spaces and math’s symbols i.e. digit and special symbols are termed as character set.
2.   In C++ programming we can say that, the characters and symbols which can easily understood and accepted by C++ program.
3.   Character set and symbols are the grouped to form the commands, expressions, words, C- statement and other tokens for C++
4.   We can also say that a C++ program is a sequence of characters and these characters from the set of character plays the different role in different way in C++ programming language.
5.   There are four categories of the character set they are as follows: -

a.   ALPHABET: -
As we know that alphabets are represented by A-Z or a-z. Because of C++ is a case sensitive programming language there for there is a different meaning for lower case and upper case.

b.   DIGITS: -
From 0-9 or combination of 0-9 is known as digits.

c.    SPECIAL SYMBOL: -
In C++ there are varieties of special symbol available, i.e. mathematical, logical, and relational operators like: +, -, *, /, \, ^, %, @, !, #, &, (, ), [, ], {, }, :, ; , , and many more.

d.   WHITE SPACES: -
Blank spaces, new line, return, horizontal tab space etc. are known as white spaces.
  
Keywords in C++: -
         As we already know about keyword in C programming language. Pre-existing, reserved words, in which each holding its own position and power and has its own specific function associated with it are knows as keywords.
There are total 63 keywords in C++ programming language in which 32 belongs to C program.
So we will divide this into two groups which make us easy to understand and remembered.
First group belongs to C, they are as follows: -

auto
const
int
short
continue
else
long
signed
case
default
register
size of
char
do
return
static
double
float
struct
unsigned
for
break
switch
void
enum
goto
typedef
volatile
extern
if
union
while



There are another 30 reserved word that were not in C, there for they are new for C++, they are as follows: -

asm
dynamic_cast
bool
explicit
catch
false
typename
class
this
using
public
throw
mutable
protected
try
typeid
namespace
reinterpret_cast
new
static_cast
operator
template
friend
private
const_cast
inline
Virtual
delete
true
wchar_t

C++ identifiers: -
1.   Variables, Classes, Functions, Structures, Arrays and other entity in C++are known as identifiers.
2.   In C++ the programmer are used to assign names of his own choice to arrays, functions, classes and other data structures are termed as identifiers.
3.   Programmers can use the different types of character sets available in C++ to create an identifier.
4.   There are some rules to create identifier or Rules for identifiers in C++.
a.   First character of identifier: -
The first character of identifier must start with a alphabet (A-Z or a-z) or underscore (_), cannot with any special symbol and any digit.
b.   No special character are allowed: -
In identifiers we can use special character like @, #, $, %, / etc, except underscore (_).
E.g. int @abc it will give error.

c.   Keywords cannot be used as identifiers: -
As we know that, keywords are reserved and each one holds a special meaning in the C++ compiler, if we use any one of them as identifier it would get a compilation error.
E.g. int goto it will give compilation error because goto is a key word.

d.   White spaces cannot used: -
While declaring identifiers, there should not be used of white space between them.
E.g. float roll no (it will show error)
         float roll_no can be used

e.   Word limit: -
While declaring an identifier word limit is necessary. Identifier must not exceed 31 characters otherwise, it will insignificant.

f.    Case sensitive: -
Upper case and lower case character in C++ have different meaning because C++ is a case sensitive programming language.
E.g int result and int RESULT are different in C++.

 Variables and Constants: Integers & Characters, Constants and Symbolic constants, Dynamic initialization of variables, reference variables, enumerated variables

 Integers and characters: -
1.   Integer is a data type, which is used for storing integer values like numbers.
2.   int is a keyword which is used to represent integer data type.
3.   It takes 4 bytes of memory space in memory.
4.   Its signed ranged is from -2147483648 to 2147483647 and unsigned range is from 0 to 4294967295.
5.   Integer is of some types like short int, int, long int, or unsigned int  all of them having different sizes and ranges.
6.   Character is a data type, which is used for storing characters like alphabets..
7.   char is the keyword which is used to represent character data type.
8.   It takes 1 bytes of memory space in memory.
9.   Its signed ranged is from -128 to 127 and unsigned range is from 0 to 255.
        

Constant: -
1.   As we know that constant refers to the values which are fixed or unchangeable, unlike variables whose value can be changed or altered.
2.   To assign a value as constant in C++, const keyword is used.
3.   Constants are also known as literals, Literals are used to express particular values within the source code of a program.
4.   Variables declared with the keyword ‘const’ become constants and cannot be altered by the program.
5.   For example a = 5;
The 5 is this piece of code was a literal constant.
6.   Literals constant can be divided into following: -

a.   Integer constant: - They are numerical constants that identify integer decimal values. (e.g. digits or its combination)

b.   Floating Point constant: - They express numbers with decimals and exponents. It can include either a decimal point, an “e” character. (e.g. value of Pi = 3.141 or exponential e = 6.02e23)

c.    Character and string constant: - There also non-numerical constants like:
‘z’         ‘p’
“Hello world”        “How do you do”
The first two expressions represent single character constants, and the following two represent string literals composed of several characters.

d.   Escape codes:
Character and string literals have certain peculiarities, like the escape codes. These are special characters that are difficult or impossible to express inside the program. List of some escape code are: -
        i.        \n   newline
      ii.        \r    carriage return
     iii.        \t    tab
     iv.        \v   vertical tab
      v.        \b   backspace
     vi.        \f    form feed (page feed)
   vii.        \a   alert (beep sound)
  viii.        \’    single quote (‘)
     ix.        \”   double quote (“)
      x.        \?   Question mark (?)
     xi.        \\   Backspace (\)

e.   Boolean constant: - There are only two Boolean values: true and false.

f.    Defined constants (#define): - We can define anything (our own names, any number, any character) as constants, by simply using the #define pre-processor directive. Its format is:
#define identifier value
For example: - #define Pi 3.14159 (now we can use Pi instead of its value, and its value cannot be change anywhere)

g.   Declared constants (const): - By using const prefix we can declare constants with a specific type in the same way as we would do with a variable:
const int width = 102;
const int height = 15;
Variables: -
1.   A variable is a value that can change, depending on conditions or on information passed to the program.
2.   Variable is container is used to store the values in our programs.
3.   In C++ variable are those, where we need to store any value either run time or compile time, and its value can be change in program.
E.g. int a=5; //declared and initialized (a is a variable with value 5)
4.   Variable is the name of the memory location which is allocated by the compiler and its size depends upon the data type of the variable.
5.   Syntax: - data-type variable, variable;
6.   There are some basic types of variable they are as follows: -
a.   bool (to store Boolean values i.e. true or false)
b.   char (to store character types)
c.    int (to store integers types)
d.   float and double (to store large number of values and also floating point)
Declaration and dynamic initialization
         Before using a variable it must be declared first. In C++ we can declared in the middle of the program because C++ follows bottom-up approach.
                 For example: -
int i;     //declared but not initialized
char c;
int i,j,k; //multiple declaration
              int i;     //declaration
i=10;    //initialization
int i=10; //declaration and initialization in one step
int i=20, j=10;
         int j = i+j; //compile time error, re-declaration a variable in same scope
Scope of variable: -
         Variables have their area of functioning, and out of that area they don’t hold their values, this area is known as scope of the variables.
         On the basic of their scope variables can be classified into two types: -
a.   Local variables
b.   Global variables
Local variable: -
         Variables which are exist within the function or block. Outside the function or block it reduces the error. Life time of local variable is until that function or block executed.
         For example: -
                  int main()
                 {
                  int m=10; 
if (m<20 o:p="">
{
int n=120; //local variable declared
cout < // print n value
}
cout < //compile time error, n not declared
}
Global variable: -
         A global variable is a variable declared in the main body of the source code, outside all function. The global function must be declared outside the main() function. Life time of the global variable is until the program is executed.
For example: -
int a;                //Global variable declared
int main()
{
x = 100;   //initialized once
cout < < ”first x=” < < x;
x= 200;    //initialized again
cout< < ”second x=” <
}
Dynamic initialization of variable: -
1.   Dynamic initialization of variable refers to initializing the value of variables at run time i.e. the initial value of variable/ object is to be provided during run time.
2.   The need of dynamic initialization of variables are as follows: -
a.   Utilization of memory is efficiently.
b.   By using overloaded formats, various initialization formats can be provided.
c.    It has the flexibility of using different formats of data at run time.
For example: -
int main()
{
int i,j;
i=10;         //Dynamic initialization at run time
j=14;         //Dynamic initialization at run time
int k=i+j;
cout < <”the value of k is” <
}
OUTPUT: - the value of k is 24
Reference variable: -
1.   A new kind of variable introduced by C++ which is known as reference variable.
2.   It provides an alternate name to the previously defined variables.
3.   It must be declared at the run time of the declaration.
4.   Syntax: - data-type &refrence_variable = variable_name
For example: -
    int xyz =100;
int &abc = xyz;   //reference variable
Enumerated variables: -
1.   An enumeration is a user-defined data type which contents an optional storage and can be assigned optional storage.
2.   The value of the storage is defined by the programmer at the time of declaring enumerated variable.
3.   Syntax: - enum enumerated_type_name{value1, value2, value3, …, valueN};
Note: - enumerated_type_name is the name of variable.
4.   enum is a keyword which is used to defined enumerated type name.
For example: -

enum grain {oats, wheats, barley};









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