What is String and operations on string ?

String:

String is a collection of characters. A string is written in double-quotation (“ ”). In C++ string is defined as an array of characters.

Declaration:

char variable_name[length];

Example:
char  chars[20];

In the above example a string variable name is declared of length 20. It means that it can only take 20 character.

Initialization:

char chars[20]= ”qwerty” ;
char chars[]= ”qwerty” ;
char chars[20]= {“q” ,”w”, ”e”, ”r”, ”t”, ”y”} ;
gets() function is used to get string input from user.

Example: 
char name[20];
gets(name);

puts() function is used to print string.
puts(name);

gets() and puts() functions are located in "string.h" library file.

What is data type and types in C++ ?

Data Type:

Data type defines a type of a variable or a value. The data is stored in a variable is according to its data type otherwise, it will generate an error.

There are main data types:

1.     int (integer)
2.     char (character)
3.     float
4.     Boolean

int data type:

int datatype is used to store the integers. It allows a variable to store an integer value. Both negative and positive numbers can be assigned to int datatype but it does not support floating values.

Example:

int roll_no = 5;
int a=-18;

char data type:

char data type is used to store a character. One character will use a 1 bit of memory.
A character is enclosed in single-quotation [‘ ‘].

Example: 

char s = ’a’;

float data type:

float datatype is used to store a numeric value with a fraction or can point value. It allows both negative and positive  numbers as well as floating values.

Example:

float  height = 5.5647;
float radius = 2.8931;

Boolean data type:

Boolean datatype has only two value “true” and “false”.  It is used for conditional statements. A Boolean variable cannot store number, integer and any other values except “true” and “false”.

What is the scope of a variable ?

Scope of variable:

The scope of variable defines the variable access point and life of variable. There are two variable scopes:

1. Local variable
2. Global variable

Local variable:

A type of variable that is declared inside a function is called as global variable.

The life of a local variable ends when a function ends and can only be accessed within the function in which it is declared.

Global variable:

A type of variable that is declared outside of any function is called as a global variable. It is generally declared after preprocessor directives and before main () function.

The life of a global variable ends when the execution of programs ends and it can be accessed by any function of the program.

Example:

#include<iostream.h>

#include<conio.h>

int a;

void main()

{ 

int b=10;

a=110;

cout<< “value of a: ”<<a ;

cout<<”\n value of b:”<<b;

getch();

}

In the above example "int a" is a globle variable which means that it can be accessed through out the program and "int b" is a local variable which means that it can only be accessed within the main(), not outside the main ().

How to declare and initialize variable in C++ ?

Variable Declaration:

The process of defining the data type and name of the variable is called variable declaration.

Example:

int marks;

Variable Initialization:

The process of assigning a value to a variable at the time of variable declaration is called as variable initialization.

Example:

Int marks =91;

Float height=5.5761;

What is a Variable and what are the rules to write a variable ?

Variable:

Variable is a quantity which means that its value is not fixed. You can understand by the name “vary” mean changing itself. In C++ variable are used to store the input and output data and also used to store the computational result.

Rules to write variable name:

1. A variable name may have character, number or (_) underscore.
2. A variable name should be start will character or (_) underscore.
3. Keywords cannot be used as variable name.
4. Special characters like $, #, !, @ cannot be used in variable name.

What is keyword in C++ ?

Keyword: 

A keyword is a special type of word which has fixed meaning and used to perform a specific operation.Keywords are written lowercase in C++. You cannot use them or redefine them because keywords have their own definition and use.

Following are some keywords used in C++:

int	struct
long	switch
register	typedef
return	union
short	unsigned
signed	void
sizeof	volatile
static	while

What are comments in C++ ?

Comments:

Comments are the non-executable and non-compilable statements. The main purpose of the comment is to add comments in your program and also used to add notes about your program to make it readable for others.

There are two types of comments in C++ :

1. Single Line Comments
2. Multi-line Comments

Single line Comments:

                           Single line comments are used to comment only one line. Double forward slashes “//” are used for single line comments.

Multi-line Comments:

                         Multi-line comments are used to comment more than one line. Multi-line comment starts with forward slash and asterisk “/*” and ends with asterisk and forward slash “*/”.