COS 126: Spring 1997 Hello World

Due: Wed. 2/12, 11:59pm

The purpose of this assignment is to familiarize you with using the computer and with the mechanics of preparing and submitting assignment solutions. This assignment carries no grade, but it should be submitted. Do this assignment even if you're already a computer whiz; it's good for you.

You should learn to use emacs for editing files, netscape for browsing the World Wide Web, lcc for compiling programs, and /u/cs126/bin/submit for submitting programs. You may be able to complete this assignment during the first or second meetings of your precept, which will be held in CS Bldg. room 101. If not, try to go to the lab (CS Bldg., room 101) when an undergraduate lab assistant is scheduled to be there (usually 8-12pm) so you can get help. Don't be afraid to ask for help; the lab assistants are paid to help you.

Your goal is to create, compile, and run the following basic program.

#include <stdio.h>

int main(void) {
	int n;

	printf("Hello world! Give me a number:\n");
	scanf("%d", &n);
	printf("Thanks for entering %d\n", n);
	return 0;
}

Completing this assignment involves the following steps. If you run into problems, ask a lab assistant for help.

• Log in to one of the SPARCStations in room 101 in the CS Bldg. After logging in, you start your first few applications by pointing and clicking with the mouse.
• When you log in, the computer starts the "Common Desktop Environment", which is a graphical user interface based on X Windows. You'll see a "Control Panel" along the bottom of the screen, and a "File Manager" window somewhere else on the screen. A tutorial window may also appear. There are lots of "Help" menus; click on a few to see what's available.
• In the left side of the Control Panel, you'll see an icon that depicts a pencil and a piece of paper. There should be a triangle above this icon; click on the icon and a pop-up menu should appear. Select "Terminal" and click the left mouse button.
• You should now have a "Terminal" window somewhere on the screen. You can enter commands by typing the commands in this or any Terminal window followed by the "Enter" or "Return" key.
• The pencil-and-paper icon denotes the text editor application. Point at it with the mouse and click on it; a Text Editor window should appear. Type the program shown above in this window; just position the mouse at the top left corner of the window and start typing. Enter program exactly as it appears above. If you omit even a comma, the program won't work. The indentation shown above is usually entered with the Tab key, but spaces work, too. When you're done, select the "File" menu on the Text Editor window and save the program in a file named hello.c.
• You can also use the emacs text editor, which is a bit more complicated, but much more powerful, and you can use emacs in terminal or telnet sessions on your own computer. To start emacs, type emacs hello.c & in the Terminal window (don't forget the &); an emacs window should appear. If you've used text editors before, you will know how to use emacs. Just use the pull-down menus and the mouse. You can also run a tutorial (look at the Help menu). Enter the program above, and save it in hello.c.
• Now type lcc hello.c (that's ell-c-c) in the Terminal window. This command runs the C compiler, lcc, which compiles hello.c and leaves an executable file named a.out in your directory. If lcc complains in some way, you mistyped something, and you should get help.
• Type a.out in the Terminal window. This command executes your program. The computer should print

  Hello world! Give me a number:

  in the Terminal window. Then it will do nothing. You must type a number (say, 5), and hit Enter, then the computer should print

  Thanks for entering 5

  and the program should terminate. You may need to repeat this edit-compile-execute cycle a few times before it all goes smoothly.
• Once you have hello.c working, submit it by typing the following command in the Terminal window.

  /u/cs126/bin/submit 1 hello.c

• If you'd like a printed copy of your program, type lpr hello.c. You can also click on the Printer icon in the Control Panel.

When you've finished this assignment, try out some of the other software you'll be using this semester. To browse the COS 126 Web pages, type

netscape http://www.cs.princeton.edu/courses/cs126/ &

You can also just type netscape &, click on netscape's Open button, and enter

http://www.cs.princeton.edu/courses/cs126/

in the pop-up dialog box. Cruise around the COS 126 Web; it is essential that you understand what's where and how to get to it.

You'll also use electronic mail a lot this semester. So, to get started, send us electronic mail telling us (briefly) whether or not you have previous programming experience, in which department at Princeton you might major, and anything else you'd like to say. To send us mail, type mail cs126, write your message, then Ctrl-d (i.e., press the Ctrl and the "d" keys simultaneously) on a line by itself to end the message. You can also terminate a message by typing a period (".") on a line by itself. Alternatively, click on the Mail icon in the Control Panel and use the graphical interface to the mail system.

Experiment with the window system by creating and resizing windows, using the mouse, etc. Send mail to a friend. Try some basic UNIX commands (ls, cd, man, mkdir, to name a few). Make sure that you get reasonably comfortable with using the computer; it's going to be your constant companion this semester.

To log out, position the mouse over the background, i.e., not over any windows, click the right mouse button, and select "Logout". Alternatively, you can just click the "EXIT" button in the Control Panel. Don't forget to log out!