Keywords Identifiers Constant in C++

Keywords:

The Keywords implement specific C++ language features. They are explicitly reserved identifiers and cannot be used as names for the program variables or other user-defined program elements.

Many of Keywords are common to both C and C+.

 

Example:            

break	auto	case
float	If	public
short	while	Int

Identifiers:

Identifiers refer to the names of variables, functions, arrays, classes , etc. created by the programmer. They are the fundamental requirement of any language. Each language has its own rules for naming these identifiers. The following rules are common to both C and C++.

·         Only alphabetic characters, digits and underscore are permitted

·         The name cannot start with a digit.

·         Uppercase and lowercase letters are distinct.

·         A declared keyword cannot be used as a variable name

 

Constant:

Constant refer to fixed values that do not changes during the execution of a program.

Like C, C++ supports several kinds of literal constants. They include integers, characters, floating point numbers and strings. Literal constant do not have memory location.

Example:

 

How constants defined in C++?

There are two ways of creating Constants in C++:

•        Using the qualifer const
• ·         Defining a set of integer constants using enum keyword

In C and C++ both , any value declared as const cannot be modified by program in any way.

Example:

Using const

 Const int num=10;

Second method  of naming integer constants is by enumeration as under;

enum { X,Y,Z}

This defines X,Y and Z as integer constants with values o,1 and 2 respectively.

This equivalent to:

const x=0;

const y=1;

const z=2;

We can also assign values to X,Y and Z explicitly.

Example:

Enum{X=100. Y=500,Z=200};

program: Write a program to swap two number.

Code:

 #include<iostream>

using namespace std;

 

 int main()

 {

 int num1,num2,temp;

 cout<<"Enter the two number ";

 cin>>num1;

 cin>>num2;

 cout<<"The number before swaping is num1="<<num1;

 cout<<" and second num2="<<num2; 

 temp=num1;

 num1=num2;

 num2=temp;

 

cout<<"\n The number after  swaping is num1="<<num1;

 cout<<" and second num2="<<num2; 

 }

OUTPUT:

Enter the two number 12

26

The number before swaping is num1=12 and second num2=26

 The number after  swaping is num1=26 and second num2=12

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