hello

A "hello world" program is a software program that prints out "Hello world!" on a display device. It is used in many introductory tutorials for teaching a programming language. Such a program is typically one of the simplest programs possible in a computer language. Some are surprisingly complex, especially in some graphical user interface (GUI) contexts, but most are very simple, especially those which rely heavily on a particular command line interpreter ("shell") to perform the actual output. In many embedded systems, the text may be sent to a one or two-line liquid crystal display (LCD), or some other appropriate signal, such as an LED being turned on, may substitute for the message.

A "hello world" program 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.

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 book The C Programming Language. The example program from that book prints "hello, world" (without capital letters or exclamation sign), and was inherited from a 1974 Bell Laboratories internal memorandum by Brian Kernighan, Programming in C: A Tutorial, which contains the first known version:

#include <stdio.h>

main() {
   printf("hello, world\n");
}

The first known instance of the usage of the words "hello" and "world" together in computer literature occurred earlier, in Kernighan's 1972 Tutorial Introduction to the Language B, with the following code:

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

There are many variations on the punctuation and casing of the phrase, and the examples on this page print out several of these variations. Variations include the presence or absence of the comma and exclamation mark, and the capitalisation of the 'H', both the 'H' and the 'W', or neither. The most commonly accepted variation nowadays, despite not being the original text, is "Hello world!"^{citation needed]} Some languages are forced to implement different forms, such as "HELLO WORLD!," on systems that only support capital letters, while many "hello world" programs in esoteric languages print out a slightly modified string. For example, one Malbolge program prints "HEllO WORld", this having been determined to be "good enough." "Hello world" programs also normally print a newline after their message.^{citation needed]}

See also

• List of hello world programs
• Fibonacci number program
• Trabb Pardo-Knuth algorithm
• Just another Perl hacker
• List of basic computer science topics

External links

• ACM "Hello World" project
• "Hello World" definition/explantion written by a programmer
• "HelloWorld online on Web, and steps beyond HelloWorld"
• Another Collection of Hello World Programs with 260+ programs, including "Hello World" in several human languages
• http://www.99-bottles-of-beer.net/ 99 bottles ... over 900 programming languages used ...
• Bootable hello world program for i386 machines
• Humor:
  • from the GNU Humor Collection
  • AsH - Hola mundo (Spanish)
• Artistic work:
  • Hello, world! A visual code for Google Earth