When we consider a C++ program, it can be defined as a collection of objects that communicate via invoking each other's methods. Let us now briefly look into what a 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, and eating. An object is an instance of a class.
· Class - A class can be defined as a template/blueprint that describes 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>
#include<conio.h>
// main() is where program execution begins.
int main(){
cout << "Hello World"; // prints Hello World
}
Let us look at
the various parts of the above program:
1. The C++
language defines several headers, which contain information that is either
necessary or useful to your
program. For this program, the header <iostream> & <conio> is
needed.
2. 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.
3. The
line int main() is the main function where program execution begins.
4. 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.
5. The
next line return 0; terminates main() function and causes it to return the
value 0 to the calling process.
Compile & Execute C++ Program:
Let's look
at how to save the file, compile and run the program. Please follow the steps
given below:
1. Open a
text editor and add the code as above.
2. Save
the file as: hello.cpp
3. Open a
command prompt and go to the directory where you saved the file.
4. Type
'g++ hello.cpp' and press enter to compile your code. If there are no errors in
your code the command prompt will take you to the next line and would generate
a.out executable file.
5. Now,
type 'a.out' to run your program.
6. You will be
able to see ' Hello World ' printed on the window.
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 you put a statement in a line. For example:
x = y;
y = y+1;
add(x,
y);
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