Hello World!

The first things most people who are just learning programming do is the pervasive "Hello World!" program. This short program's prevalence is so extensive because it demonstrates a language's structure and syntax. Specifically it shows how to print something to the screen and how to run a program.

Python


print "Hello World!"


C++


#include <iostream>
using namespace std;

int main()
{
    cout << "Hello World!" << endl;
}


Java


class HelloWorld {

    public static void main(String[] args) {

        System.out.println("Hello World!");
    }

}

• As you can see, Python's syntax is the simplest. There is no necessary structure, and all you have to do is type "print [thing to be printed (in single or double quotes)]"
• C++'s syntax is more complicated, but it is by no means convoluted. 
• In order to use cout (the C++ equivalent of print) you must include the iostream library. 
• However, just including the library isn't enough. You have to tell the pre-processor which part of iostream it needs to look in to use cout. This is why we include the "using namespace std;" line. 
• Finally, because C++ is an object-oriented program, every script you write must have a main function.  The convention is for main to have a return type of int and for all of the Also, every functions' code is contained within curly braces.
• Java is based on C++, so it has a lot of the same conventions (such as ending every statement in a semi-colon). However, it is even more object-oriented (in that every script is a class, which creates an object when compiled). 
• Because everything in Java is a class, everything that can be done in Java is accomplished through method calls to a class.
• When printing, System is a class (first letter is upper case and multiple words written with camel case by convention), which contains an out method and a println method.
• You'll recognize that main is still required, but now you have to declare it with public, static, and void, rather than just int. It also contains two parameters: String[] and args.