hello.html

Exercise Hello-World

Objective: Create a working programming environment and make a Hello-World program.

Get yourself an account on IFA computer system.
Boot your Ubuntu system e.g. from the CD.
Prepare the directory for the exercises:
- Open a terminal window (in Gnome: Applications→Accessories→Terminal) and login into lifa.phys.au.dk (or, better, genryc if you are inside IFA's firewall). If your login name is jensen, do
```
ssh -X jensen@lifa.phys.au.dk
```
  (the -X option is if you plan to use X-windows programs). After typing your password do
```
mkdir ~/public_html
mkdir ~/public_html/numeric
        
```
  ("~/" is an abbreviation for you home directory). Now the URL "http://www.phys.au.dk/~jensen" points to your"~/public_html/" directory, while "http://www.phys.au.dk/~jensen/numeric" points to your"~/public_html/numeric" directory which should then be the place for your solutions to the exercises. Remember to do
```
chmod -R go+xr ~/public_html
```
  to allow everybody to see your files in this directory. You might need to issue this command again after you have created some new files.
Pick your favourite programming language for the exercises. If there is a debian package for it (I'll be surprised if there isn't), I'll install it on genryc, otherwise you are on your own. If you do not have strong preferences, I suggest Javascript -- it's the easiest modern language to learn; or C -- it's probably the most ubiquitous language in existence, it's fast, and there is GNU Scientific Library written in C.
Pick your favourite editor to edit your programs. If you don't have one, try the following editors available on lifa and genryc: nano (very simple), jed (more advanced), gedit (simple graphical interface, you probably want this one), emacs (popular with computer programmers), vi (good old stuff from 1976, still going strong), kate (KDE advanced text editor)...
Create a Hello-World program in your favourite programming language with your favourite editor and build it using make utility. In C:
- mkdir ~/public_html/numeric/hello
- cd ~/public_html/numeric/hello
- create a file hello.c with the content
```
#include <stdio.h>
int main() {
	printf("Hello, world\n");
	return 0;
}
```
- create a file makefile with the content
```
hello.txt: hello       # hello.txt is the default target
	./hello > hello.txt # run hello and redirect stdout into hello.txt
	cat hello.txt       # send the content of hello.txt to stdout

hello: hello.o
	cc hello.o -o hello

clean:
	rm -f hello hello.o hello.txt
	
```
  Note that the indented lines start with a tab-character, not with spaces.
- Now run the make utility
```
 make 
```
  you should see the message on your screen if everything goes right (it never does the first time, of course...).
- You can find other hello-world examples here. Note that some compilers are only installed on genryc, not lifa.
Send me an email with the URL of your exercises, when you are done.