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:
mohd
zara
abc
move_name
a_123
myname50
_temp
j
a23b9
retVal
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.