Basics of C++

Today we will see the basics of C++:

When we consider a C++ program it can be defined as a collection of objects that communicate via invoking each others methods.

Let us now briefly look into what do class, object, methods and instant variables mean.

Object - Objects have states and behaviors.

Example: A dog has states-color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class.

Class - A class can be defined as a template/ blue print that describe the behaviors/states that object of its type support.

Methods - A method is basically a behavior. A class can contain many methods.

It is in methods where the logics are written, data is manipulated and all the actions are executed.

Instant Variables - Each object has its unique set of instant variables. An object's state is created by the values assigned to these instant variables.

C++ Program Structure:

Let us look at a simple code that would print the words Hello World.

#include <iostream>

using namespace std;
// main() is where program execution begins.
int main()
   cout << "Hello World"; // prints Hello World
   return 0;

Let us look various parts of the above program:

The C++ language defines several headers, which contain information that is either necessary or useful to your program.

For this program, the header <iostream> is needed.

The line using namespace std; tells the compiler to use the std namespace. Namespaces are a relatively recent addition to C++.

The next line // main() is where program execution begins. is a single-line comment available in C++.

Single-line comments begin with // and stop at the end of the line.

The line int main() is the main function where program execution begins.

The next line cout << "This is my first C++ program."; causes the message "This is my first C++ program" to be displayed on the screen.

The next line return 0; terminates main() function and causes it to return the value 0 to the calling process.

Make sure that g++ is in your path and that you are running it in the directory containing file hello.cpp.

You can compile C/C++ programs using makefile.

Semicolons & Blocks in C++:

In C++, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.

For example, following are three different statements:

x = y;

y = y+1;
add(x, y);

A block is a set of logically connected statements that are surrounded by opening and closing braces.

For example:

   cout << "Hello World"; // prints Hello World
   return 0;

C++ does not recognize the end of the line as a terminator. For this reason, it does not matter where on a line you put a statement.

For example:

x = y;

y = y+1;
add(x, y);

is the same as

x = y; y = y+1; add(x, y);

C++ Identifiers:

A C++ identifier is a name used to identify a variable, function, class, module, or any other user-defined item. An identifier starts with a letter A to Z or a to z or an underscore (_) followed by zero or more letters, underscores, and digits (0 to 9).

C++ does not allow punctuation characters such as @, $, and % within identifiers.

C++ is a case sensitive programming language. Thus, "Manpower" and "manpower" are two different identifiers in C++.

Here are some examples of acceptable identifiers:



Whitespace in C++:

A line containing only whitespace, possibly with a comment, is known as a blank line, and C++ compiler totally ignores it.

Whitespace is the term used in C++ to describe blanks, tabs, newline characters and comments.

Whitespace separates one part of a statement from another and enables the compiler to identify where one element in a statement, such as int, ends and the next element begins.

Therefore, in the statement,

int age;

There must be at least one whitespace character (usually a space) between int and age for the compiler to be able to distinguish them. On the other hand, in the statement

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

No whitespace characters are necessary between fruit and =, or between = and apples, although you are free to include some if you wish for readability purpose.

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