An introduction to syntax, printing, and entry points.
The “Hello World!” program is the first step in learning how
to code with any language. This tradition was first established in
the 70s by Nokia Bell Labs and has since advanced into the famous
first line of code that most programmers write. It is a program that
prints the text “Hello World!” to some output stream, usually the
console, and it’s primarily taught for three purposes:
To illustrate the basic syntax of a language
To check that you have correctly installed your computer
language.
To teach printing
Printing is a handy tool because you can use it for
debugging regardless of what language or IDE you are running
Here are some examples of how printing works:
Code:
print("Hello World!")
Output:
> Hello World!
Code:
System.out.println("Hello World!");
Output:
> Hello World!
Code:
cout << "Hello World!";
Output:
> Hello World!
Code:
print("Big thank you to all contributors to Hour of Code!")
Output:
> Big thank you to all contributors to Hour of Code!
Code:
System.out.println("Big thank you to all contributors to Hour of Code!");
Output:
> Big thank you to all contributors to Hour of Code!
Code:
cout << "Big thank you to all contributors to Hour of Code!";
Output:
> Big thank you to all contributors to Hour of Code!
Code:
print("I like to eat pizza!")
Output:
> I like to eat pizza!
Code:
System.out.println("I like to eat pizza!");
Output:
> I like to eat pizza!
Code:
cout << "I like to eat pizza!";
Output:
> I like to eat pizza!
Note: When you print text, everything between the quotation marks is
printed to the output.
Entry points
Another important beginner concept is entry points. Entry
points are where your program will begin to run. In Java and C++,
the main function/method (you will learn more about functions
and methods later) marks this entry point. That means to get the
“Hello World!” examples from above to run in these languages, you
will need to put your code inside the brackets after the main
function/method. The entry points for getting our previous printing
code to run are marked below; only code after the entry point will
run.
Code:
public class HelloWorld{
public static void main(String[] args)
{
// THIS IS THE ENTRY POINT
System.out.println("Hello World!");
}
}
Output:
> Hello World!
Code:
#include <iostream>
using namespace std;
int main()
{
// THIS IS THE ENTRY POINT
cout << "Hello World!";
return 0;
}
Output:
> Hello World!
Python is executed differently from Java and C++. It simply runs all
code from the very first line to the very bottom line, and this
means you don’t need to mark any entry points like in Java or C++.
The same python code from before, copied below for convenience, will
run fine.
Code:
print("Hello World!")
Output:
> Hello World!
Note: It’s possible to structure your code in Python to define an
entry point that isn’t the first line, but it isn't necessary to get
the code running. In Java and C++, you need to define an entry
point, or your code will not run.
Many of the future articles won’t include marked entry points
because they take a lot of space and don’t add much instructional
value, but it’s essential to know that if you want to get code
running on your computer, you will need to use entry points for Java
and C++.
You can play with all the code we've used in this article on Replit: