Overview of the Basic Structure of C++ Programming

• The // in first line is used for representing comment in the program.
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• The second line of the program has a # symbol which represents the preprocessor directive followed by header file to be included placed between < >.
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• The next structure present in the program is the class definition. This starts with the keyword class followed by class name employee. Within the class are data and functions. The data defined in the class are generally private and functions are public. These explanations we will be detailed in later sections. The class declaration ends with a semicolon.
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• main() function is present in all C++ programs.
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• An object e1 is created in employee class. Using this e1 the functions present in the employee class are accessed and there by data are accessed.
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• The input namely ename and eno is got using the input statement namely cin and the values are outputted using the output statement namely cout.

Variable, Constants and Data types in C++

In this C++ tutorial, you will learn about variable, constants and data types in C++, rules for defining variable name, short int, int, long int, float, double, long double, char, bool, declaring variables and constants.

Variables 

A variable is the storage location in memory that is stored by its value. A variable is identified or denoted by a variable name. The variable name is a sequence of one or more letters, digits or underscore, for example: character _


Rules for defining variable name:

• A variable name can have one or more letters or digits or underscore for example character _.
• White space, punctuation symbols or other characters are not permitted to denote variable name. .
• A variable name must begin with a letter.
  
• Variable names cannot be keywords or any reserved words of the C++ programming language.
  
• C++ is a case-sensitive language. Variable names written in capital letters differ from variable names with the same name but written in small letters. For example, the variable name KHAN differs from the variable name khan.

As previously explained, a variable is the storage location in memory that is stored by variable value. The amount of memory allocated or occupied by each variable differs as per the data stored. The amount of memory used to store a single character is different from that of storing a single integer. A variable must be declared for the specific data type.

Data Types

Below is a list of the most commonly used Data Types in C++ programming language:

• short int
• int
• long int
• float
• double
• long double
• char
• bool

short int : This data type is used to represent short integer.

int: This data type is used to represent integer.

long int: This data type is used to represent long integer.

float: This data type is used to represent floating point number.

double: This data type is used to represent double precision floating point number.

long double: This data type is used to represent double precision floating point number.

char: This data type is used to represent a single character.

bool: This data type is used to represent boolean value. It can take one of two values: True or False.

Declaring Variables: In order for a variable to be used in C++ programming language, the variable must first be declared. The syntax for declaring variable names is

data type variable name;

The date type can be int or float or any of the data types listed above. A variable name is given based on the rules for defining variable name (refer above rules).

Example:
int a;
This declares a variable name a of type int.

If there exists more than one variable of the same type, such variables can be represented by separating variable names using comma.

For instance:

int x,y,z;

This declares 3 variables x, y and z all of data type int.

The data type using integers (int, short int, long int) are further assigned a value of signed or unsigned. Signed integers signify positive and negative number value. Unsigned integers signify only positive numbers or zero.

For example it is declared as

unsigned short int a;
signed int z;

By default, unspecified integers signify a signed integer.

For example:

int a; is declared a signed integer
It is possible to initialize values to variables:

data type variable name = value;

Example:
int a=0;
int b=5;


Constants 
Constants have fixed value. Constants, like variables, contain data type. Integer constants are represented as decimal notation, octal notation, and hexadecimal notation. Decimal notation is represented with a number. Octal notation is represented with the number preceded by a zero character. A hexadecimal number is preceded with the characters 0x.

Example:

80 represent decimal
0115 represent octal
0x167 represent hexadecimal
By default, the integer constant is represented with a number.
The unsigned integer constant is represented with an appended character u. The long integer constant is represented with character l.

Example:

78 represent int
85u present unsigned int
78l represent long
Floating point constants are numbers with decimal point and/or exponent.

Example 2.1567 4.02e24 These examples are valid floating point constants.
Floating point constants can be represented with f for floating and l for double precision floating point numbers.
Character constants have single character presented between single quotes.


Example


‘c’ ‘a’ are all character constants.
Strings are sequences of characters signifying string constants. These sequence of characters are represented between double quotes.

Example: “Manoj Patel” is an example of string constant.