C++ Basic Syntax

In a C++ program, objects communicate by invoking each other's methods, forming a cohesive system. Let's delve into the meanings of classes, objects, methods, and instance variables.

Object:

• Objects have states and behaviours. For example, a dog can have states like colour, name, and breed, and behaviours like wagging, barking, and eating. Essentially, an object is an instance of a class.

Class:

• A class serves as a blueprint or template that defines the states and behaviours that its objects will have.

Methods:

• Methods define behaviours in a class. A class can contain multiple methods, where the logic is implemented, data is manipulated, and actions are carried out.

Instance Variables:

• Each object has a unique set of instance variables. The state of an object is determined by the values assigned to these variables.

 

Structure of a C++ Program

Let's look at a simple example that prints "Hello World":

#include <iostream>

using namespace std;

 

// Program execution begins here.

int main()

{

   cout << "Hello World"; // Prints Hello World

   return 0;  

}

 

Components of the Program

• Header Files: C++ defines several headers that provide essential functionalities. For this program, we include the <iostream> header.
• Namespace: using namespace std; tells the compiler to use the standard namespace, which helps avoid naming conflicts.
• Comments: The line // main() is where program execution begins. is a single-line comment. Single-line comments in C++ start with //.
• Main Function: int main() defines the main function where execution starts.
• Output Statement: cout << "Hello World"; prints "Hello World" to the screen.
• Return Statement: return 0; ends the main function and returns 0, signaling successful execution.

 

Compiling and Running a C++ Program in Dev-C++

Here’s how to save, compile, and run the program using Dev-C++:

1. Open Dev-C++ and create a new source file.
2. Write the code shown above.
3. Save the file as hello.cpp.
4. Click on the "Execute" menu and select "Compile & Run" (or press F11).

You should see Hello World printed in the output window.

   

Semicolons and Blocks in C++

In C++, statements end with a semicolon (;), marking the conclusion of one logical statement. For instance:

a = b;

b = b + 1;

sum(a, b);

 

A block is a set of statements enclosed in braces ({}). For example:

{

   cout << "Hello World"; // Prints Hello World

   return 0;

}

 

C++ does not consider the end of a line as a statement terminator, so statements can be written on the same line:

a = b; b = b + 1; sum(a, b);

 

Identifiers in C++

Identifiers are names for variables, functions, classes, modules, and other user-defined items. They must begin with a letter (A-Z or a-z) or an underscore (_) and can be followed by letters, digits (0-9), or underscores. Identifiers are case-sensitive.

Examples of valid identifiers:

ram	mohan	john	variable_name	x_123
Example15	_temp	y	z9value	returnValue

 

Keywords in C++

The following are reserved words in C++, meaning they cannot be used as identifiers:

asm	else	new	this
auto	enum	operator	throw
bool	explicit	private	TRUE
break	export	protected	try
case	extern	public	typedef
catch	FALSE	register	typeid
char	float	reinterpret_cast	typename
class	for	return	union
const	friend	short	unsigned
const_cast	goto	signed	using
continue	if	sizeof	virtual
default	inline	static	void
delete	int	static_cast	volatile
do	long	struct	wchar_t
double	mutable	switch	while
dynamic_cast	namespace	template

        

Whitespace in C++

Whitespace includes blanks, tabs, newline characters, and comments, and it separates parts of a statement to help the compiler distinguish between elements like int and value:

int value;

In the following example, whitespace is not necessary but can improve readability:

total = apples + oranges;   // Calculate the total fruit

This deeper understanding of C++ fundamentals will aid in writing, compiling, and executing C++ programs effectively.