Hello World!

A “Hello world” program is a computer program that outputs “Hello world” on a display device. Because it is typically one of the simplest programs possible in most programming languages, it is by tradition often used to illustrate to beginners the most basic syntax of a programming language. It is also used to verify that a language or system is operating correctly. In a device that does not display text, a simple program to produce a signal, such as turning on an LED, is often substituted for “Hello world” as the introductory program.

Purpose

A “Hello World” program has become the traditional first program that many people learn. In general, it is simple enough so that people who have no experience with computer programming can easily understand it, especially with the guidance of a teacher or a written guide. Using this simple program as a basis, computer science principles or elements of a specific programming language can be explained to novice programmers. Experienced programmers learning new languages can also gain a lot of information about a given language’s syntax and structure from a hello world program. In addition, “Hello World” can be a useful sanity test to make sure that a language’s compiler, development environment, and run-time environment are correctly installed. Configuring a complete programming toolchain from scratch to the point where even trivial programs can be compiled and run can involve substantial amounts of work. For this reason, a simple program is used first when testing a new tool chain. “Hello world” is also used by computer hackers as a proof of concept that arbitrary code can be executed through an exploit where the system designers did not intend code to be executed—for example, on Sony’s PlayStation Portable. This is the first step in using homemade content (“home brew”) on such a device.

History

While small test programs existed since the development of programmable computers, the tradition of using the phrase “Hello, world!” as a test message was influenced by an example program in the seminal book The C Programming Language. The example program from that book prints “hello, world” (without capital letters or exclamation mark), and was inherited from a 1974 Bell Laboratories internal memorandum by Brian Kernighan, Programming in C: A Tutorial,[1] which contains the first known version:


 main()
 {
        printf("hello world");
 }

The C version was adapted from Kernighan’s 1972 A Tutorial Introduction to the Language B,[2] where the first known version of the program is found in an example used to illustrate external variables:


 main(){
   extrn a,b,c;
   putchar(a); putchar(b); putchar(c); putchar('!*n');
   }
 
 a 'hell';
 b 'o, w';
 c 'orld';

The program prints "hello, world!" on the terminal, including a newline character. The phrase is divided into multiple variables because in B, a character constant is limited to four ASCII characters. The previous example in the tutorial printed “hi!” on the terminal, so the phrase "hello, world!" was originally introduced as a slightly longer greeting that required several character constants for its expression. It is also claimed that “hello, world” originated instead with BCPL (1967).[3] For modern languages, the hello world program tends to subtly grow in sophistication. For example, the Go programming language introduced a multilingual hello world program,[4] Sun demonstrated a Java hello world based on scalable vector graphics,[5] and the XL programming language features a spinning Earth hello world using 3D graphics. Text content from the Wikipedia article covering the Hello World Program.



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